The transmission of the carrot mosaic virus (CMV) by the aphidsAcyrtJiosiphon pisum HARRÍS,Cavariela aegopodii SCOP, andMyzus persicae SULZ was proved experimentally. It was observed simultaneously that CMV has a non-persistent character. CMV can be transmitted already 2 min after acquisition feeding by the aphidsMyzus persicae SDLZ andCavariella aego-podii Scop. When the time of acquisition feeding is prolonged to 4 min, CMV is transmitted also by aphidAcyrthosiphon pisum HAREÍs. The host range of the investigated virus wasalso determined and its transmission to 8 plant species, belonging to 4 families, was achieved. On the basis of studies of the vector virus relationship and of the host range, further proof was given for the different character of the Australian Carrot motley dwarf virus, theApivm virus 1 Roland and CMV. The experiments showed that preliminary starving of the aphids for 1 h increases their ability to transmit the virus by 3-3%.

Antiserum against the X virus inhibitor was prepared by immunizing rabbits with the inhibitor antigen obtained in two ways: (1) ultracentrifugation of potato leaf sap in a Spinco L for 1 h at 40000 r.p.m., (2) ultracentrifugation and fractionation of the sap on a Sephadex G-50 column.
The antiserum is specific against the inhibitor protein and does not react with other proteins of the plant or with the X virus. Direct serological analysis makes it possible to determine in the potato leaf sap either the presence or the absence of the X virus inhibitor, to follow the degree of inactivation of the inhibitor due to various factors and finally to determine the relative amount of inhibitor in various cultivars and hybrids of the potato plant.
A detailed description of the method for determining the amount of the X virus inhibitor in the leaf sap from various potato cultivars and hybrids is given. The amount of sap required for analysis is very small (1-2 ml) which makes it possible to carry out analyses on individual plants. The duration of analysis is about 1 h.
The determination of the inhibitor amount in the potato leaf sap agrees with that of the inhibitory potency of the cell sap in 87.7% cases.

The author intended here to present a classification of discontinuous, particulate membraneous structures of the plant cell, including (1) dense bodies, (2) vacuoles, (3) vesicles in plastids and mitochondria, (4) vesicles outside the protoplast and (5) vesicles surrounded by a compound (double) membrane. Three types of dense bodies (1) are distinguished: (a)Mühlethaler's spherosomes, including phragmosomes (b) lipoid bodies and (c) classical spherosomes. Type (a) is characterized in particular by being clearly bounded by the unit membrane; the matrix of these structures after ordinary treatment is grey in the positive and shows a more or less visible internal structure, the bodies are round in shape. Types (b) and (c), on the other hand, are frequently described as membrane-less structures, their matrix being very dark in the positive, frequently with a dark fringe and a lighter central part. They show no other structure and are mostly irregular in shape which is apparently an artifact. Bodies of type (a) are undoubtedly the immediate component of active living matter which cannot be said about types (b) and (c).Frey-Wyssling's interpretation of spherosomes need not be generally valid for all dense bodies, other explanations being acceptable. It is thus possible to interprot spherosomes as promitochondria and "preproplastids".
The present manuscript is a torso where only the dense bodies have been treated in greater detail A chronological review of the literature opens the manuscript, dealing mainly with the descriptive morphology of these structures. This section is published in extenso. In the other section-unfinished-the functional morphology of the dense bodies was to be presente d. From this section only the conclusions concerningMühlethaler's spherosomes are published.

The action of zinc on the growth of barley and the biosynthesis of indol compounds and gibberellin-like substances was investigated in a number of concentrations of zinc from doses stimulating growth to toxic doses. The seeds were soaked before sowing in solutions of zinc sulphate (5.10^-5 to 5.10^-1% Zn), and the plants cultivated for 7 days in water. Lower concentrations of zinc increased both plant growth and the biosynthesis of tryptophan and auxins. At the optimum concentration of 5.10^-3% Zn this increase in tryptophan amounted to 241% of the variant without zinc; in substances with an R_F corresponding to indolyacetic acid, the increase determined by the biological test, was 207% as against the variant without zinc. Higher concentrations of zinc inhibited growth, the tryptophan content was decreased to below that of the control without zinc and the auxin content also fell to below the control values. Zinc also influenced the content of gibberellin-like substances in the plants. At a concentration of 5.10^-3% Zn the increase in the growth activity in the gibberellic acid area of the chromatogram was 294% of the variant without zinc. At toxic concentrations of zinc, the content of gibberellin-like substances fell to below that of the controls. The finding that zinc acts simultaneously on the biosynthesis of auxins and gibberellins is also evidence for the common action of growth substances of various chemical types on plant growth.

In this paper the values of photosynthetic intensities of spring barley leaves measured by two different methods were compared:
1. By the gravimetric method of Bartoš, Kubín and Šetlík (1960), modified by Nátr and Špidla (1961) for cereal leaves. Segments were laid on a special support and illuminated for several hours from a constant source of light. The tissues were completely saturated with water, the temperature and the flow-rate of the air were also constant. Photosynthetic intensity is expressed as the increase of dry matter in segments in mg per dm² of a double area of leaf, and per hour. The weight increase of the dry matter is converted to values corresponding to CO₂ consumption by means of a coefficient: 0.64 mg of dry matter correspond to 1 mg of CO₂, or, 1 mg of dry matter corresponds to 1.56 mg of CO₂.
2. By the gazometric method of measurement of CO₂ consumption, expressed in mg per dm² of double area of leaf, and per hour. For these measurements an infrared analyser was used under the following conditions: open system, constant illumination, temperature (25°C) and air humidity (45%), as well as constant CO₂ content in the air (0.033 vol.%).
The results prove that in most instances both methods afford, from the quantitative point of view, completely corresponding results. As a cause of a few discrepancies met in some experiments, the influence of cutting off of the leaves and uneasily seizable differences in experimental conditions during the exposure of leaves and segments can be considered. Further, the calculated value for the conversion coefficient, i.e. 0.64, must not in every case necessarily correspond to the chemical composition of formed assimilates. The existence of inhibitory influence of accumulated assimilates in leaf segments on the photosynthetic intensity can be excluded.
When the CO₂ consumption of cut off and non-cut leaves of the same experimental plant was measured, no differences could be observed.
The advantages and possibilities of the use of dry matter increment determination in segments as a measure of photosynthetic intensity are discussed.

Investigating weeds for viruses in ruderal localities of Greater Prague two forms of mosaic diseases inSisymbrium loeselii Jusl. were demonstrated (green and yellowish-green mosaic). Transmission tests carried out on differential host plants showed that the green mosaic is caused by cabbage black ringspot virus (CBRV) and the yellowish green by mixed infection of CBRV and tobacco mosaic virus (TMV).
TMV-isolate is characterized as an unusual necrotic strain; its capability to reproduce in cruciferous plant in nature is unique.
It was ascertained that green mosaic was commonly spread overSisymbrium plants in ruderal ***DIRECT SUPPORT *** A01GP029 00004 associations on Prague territory; epidemiological significance of this discovery is discussed.

A technical procedure is described together with slight modifications and technical alternations, for the application of the quantitative serological method in work with labile plant proteins, particularly those from vegetative organs.
The procedure is based on the well-known method developed byBoyden et al., usingLibby's "photronreflectometer". The results published here have been obtained in the course of the determination of applicability of the following modifications to a quantitative evaluation of serological reactions:
a) The use of "acetone preparations" in obtaining antigens: A single operation is sufficient to remove undesirable admixtures, such as lipids, organic acids, tannin, alkaloids etc., the antigenic activity of the protein material being preserved. The conservability of such material in a dry state is considerably increased (for a number of months) by this procedure.
b) Stabilization of solutions of plant antigens of adding 5% fructose: The denaturation of plant proteins in frozen solutions is thus to a high degree prevented and their applicability is prolonged for a number of days.
c) A modification of incubation period and temperature during quantitative precipitation in order to ensure a more precise standardizing of the experimental conditions, with simultaneous decreasing of the antiserum doses.
d) Standardization of the calibrating process ofLibby's "photronreflectometer".
e) Application ofRunge's physiological solution; addition of ascorbic acid to prevent melanin formation in antigen extracts from plant material.

1. In tetraploid Phaseolus sp. × P. calcaratus cross, shrivelled but viable seeds were produced. One hybrid was raised but it died within a month. Another hybrid was raised to flowering by artificially culturing the embryos before shrivelling.
2. The F₁ of tetraploid Phaseolus sp. × P. calcaratus cross, had various leaf abnormalities at an early stage. In most of the characters the hybrid was intermediate between the two parents. The twining habit of P. calcaratus dominated in the hybrid. The F₁ plant had 10.7 per cent pollen fertility. The hybrid died within a week of flowering.
3. In P. calcaratus × tetraploid Phaseolus sp. cross, rudimentary, non-viable seeds were produced.
4. The incompatibility barriers are active - (a) at post-fertilization stages causing shrivelled and rudimentary seeds and (b) in the F₁ generation causing hybrid lethality and sterility. The importance of embryo culture techniques in removal of the first type of crossability barriers is stressed.

The dense vacuoles, considered to be the classic Golgi apparatus in the root meristem ofFagopyrum, were studied by the following methods: 1. Impregnation methods for the demonstration of the Golgi apparatus, 2. cytochemical methods, 3. electron microscopic methods in the light microscope and 4. the electron microscope. A comparison was made with the classic Golgi apparatus in animal cells in the light and electron microscope.
Dense vacuoles inFagopyrum and also evidently in other plants, were taken for the classic Golgi apparatus on account of their morphological similarity to the Golgi apparatus in animal cells on impregnation with silver and osmium and their staining preperties with lipoid methods. Dense vacuoles differ from the classic Golgi apparatus in other chemical properties, such as content of phenol substances, etc. No formations were found in animal cells which were similar to dense vacuoles on investigating by electron microscopy. In the electron microscope dense vacuoles have the appearance of derivatives of the normal light vacuoles known in plant cells. They therefore belong to vacuome of plant cell and cannot be analogous to the classic Golgi apparatus in animal cells. Thus the use of the term Golgi apparatus for dense vacuoles is not well founded.
A comparison was made of fixation and impregnation used in the light microscope with fixation in the electron microscope. After fixation with permanganate, dense vacuoles have the same shape as after impregnation. After fixation with permanganate, they stain an intense black in the same way as after impregnation with silver and osmium. The form of the vacuoles is dependent on the fixation used. The comparison was made in the light microscope.

For specific staining of TMV inclusions the cytochemical method of Hršel for the determination of tryptophan containing proteins was used. This method makes it possible to obtain series of sections in contrast to the methods employed up to the present, so that TMV inclusions from any part of the plant can be detected. Staining was tested "in situ" as well as in preparations of isolated virus particles.

The polymorphism of the dictyosomes in the root meristeme ofFagopyrum is connected with their various functions in secretory processes and cell differentiation. The dictyosomes containing vesicular dilatations of the cisternae, which in this object occur more frequently than in others, probably participate in a similar way as the Golgi apparatus of the animal cell in the formation of lysozomes, in the formation of elements belonging to the group of dense bodies analogical lysozomes. These bodies are present in large numbers in the cytoplasm of cells, containing dictyosomes with vesicular dilatations. The other forms of the dictyosomes reveal indications of their participation in the production of the carbohydrate material of the cell walls, like most dictyosomes of other plant objects. However, no fusion of the Golgi vesicles with the plasmalemma was observed. According to their morphological appearance the typical forms of dictyosomes were classified on the basis of their relationship to secretory processes. Simultaneously the morphology and function of the Golgi apparatus was compared in the animal and plant cell. Several morphological varieties of the dictyosomes of plant cells, observed after the action of pathogenic factors and the effect of the fixation procedures, were also noticed in small quantities in the cells of the investigated objects.

The relationship of the membrane structure, designated in electron microscopy as the Golgi apparatus, to the classic Golgi apparatus in the light microscope were studied withFagopyrum. Comparison of these structures in plant cells with the same or similar structures in animal cells led to the following conclusions: there exist two groups of formations, impregnable with osmium or silver, considered as the classic Golgi apparatus. The first group contains the active membrane structures. These are the dictyosomes and the anastomosing form of the electron microscopic Golgi apparatus. To this group belongs also the endoplasmatic reticulum, which in plant cells forms dense vacuoles, having the appearance of the classic Golgi apparatus, and in animal cells occasionally has a similar arrangement as the anastomosing form of the Golgi apparatus. The second group comprises formation containing reserve and secretion material, i.e. predominantly products of the activity of the electron microscopic Golgi apparatus and of the endoplasmic reticulum (matter of the dense vacuoles, lipochondria, secretory granula etc.).
In the plant cells, especially ofFygopyrum, the dictyosomes contained in the structures of the first group are separated from the formations of a reserve character in the second group, formed in the lumen of the endoplasmic reticulum (dense vacuoles). The identity of the dictyosomes with the osmiophilic platelets, considered by some authors in the light microscope as the classic Golgi apparatus, has not been proved up to present, because of the one-sidedness of the methods used nowadays. WithFagopyrum no foundation has been observed for the assumed formation of net-form structures by grouping of the dictyosomes. Structures similar to the net-form of the classic Golgi apparatus in the animal cell form only dense vacuoles.
On the basis of the differentiation of both types of formations in the plant cell, the foundations were laid for the characterization of the classic Golgi apparatus in the animal cell. The net-form of the classic Golgi apparatus in the animal cell is obviously not artificial, but reflects the ultrastructural arrangement of the electron microscopic Golgi apparatus or of the endoplasmic reticulum.
The problem of the suitability and specification of the name Golgi apparatus in the animal and plant cell was also discussed. In contrast to the opinion of some authors, it does not appear useful to remove the name golgi apparatus, designating the dictyosomes and the anastomosing forms of the smooth membranes.

The purpose of this paper is to compare some results achieved in the enzymatic decay of beech wood meal and holocelulose affected by mycelium-free culture filtrate of wood destroying fungusSchizophyllum commune. The fungus had been obtained from the Institute of Plant Physiology, J. E. Purkyně University, Brno.

When the epicotyl and one cotyledon is cut off from pea seedlings, only the axillary of the amputated cotyledon is known to grow. When³²P is applied to the roots of such plants, then a higher radioactivity appears in the axillary of the amputated cotyledon already 24 hrs. after amputation of one cotyledon, although this axillary is of the same size at this time as that of the remaining cotyledon. This fact indicates a more extensive material transport to the axillary bud of the amputated cotyledon already during the first day after amputation
The effect of individual regulators on the³²P transport was investigated in an experiment where pea seedlings cultivated in the dark were decapitated and a 0.5% paste, containing the regulatory compounds was placed either on the cutting surface in the apical part of the epicotyl stump or in its central part. After a week the plant roots were supplied with³²P and its transport to the upper part of the epicotyl stump was followed. This transport increased about 10-fold in the case of a paste, containing indolyl acetic acid, when the paste was spread on the apical cutting surface of the stump. However, the transport was inhibited when the paste was applied in the central part of the stump. These results indicate that only the transport of³²P towards the paste with indolyl acetic acid is accelerated, whereas it is decelerated above this paste. A paste, containing triodobenzoic acid inhibited³²P transport only when applied to the apical cutting surface of the epicotyl stump and not when spread over the middle part. In this case³²P transport was more rapid above the paste than towards the paste. The situation was similar in the case of gibberellin and kinetin.

Humus acid (Humussäure Riedel de Haen AG. Seelze Hannover) in 0.01% concentration increases the respiration intensity of plant roots grown in water cultures both as regards O₂ consumption and CO₂ production, while RQ (CO₂:O₂) is only very slightly increased. The plants used in these experiments were the winter wheat Pyšelka (Triticum vulgare Vill.), maize Zaj íček's "Český koňský zub" (Zea mays L.) and the gourd Veltrusská velkoplodá (Cucurbita maxima L.). O₂ consumption and CO₂ production were determined on separated root tips by the direct Warburg method. It was found that the effect of humus acid is not only to increase respiration intensity in the roots of the experimental plants, but also their lengths and dry weights (for all experimental plants); for maize and gourd the dry weights of overground parts were also increased, which indicates that increased respiration intensity was linked with more intensive growth of the plants.

Lucerne plants in the first crop year as well as plants of spring wheat from different sites of the respective experimental plots showed differences in sap exudation from detopped roots or from stumps of the main shoots, reflecting differences in properties of the soil profile. The differences in sap exudation were observed at a time when the plants did not show any visible differences in water availability.
Differences in the water potential deficit of the leaf blades of lucerne plants in the second crop year and of sugar beet plants, related to differences in soil profile properties, were observed in another series of experiments. Sugar beet plants showed a higher physiological lability than lucerne plants.
The sites characterized by unfavourable plant-water-relations usually gave lower yields. The coefficients of variability for the yields of lucerne fresh matter from irrigated plots were three times lower than those for yields from plots without irrigation, influenced by soil heterogeneity.

Many studies have been made on ribosomes both in plant and animal material, on account of their importance in the proteosynthesis of protein. In plant material, studies have been made on the pea by Ts'o andBonner (1956), Ts'o,Bonner andVinograd (1958),Setterfield et al. (1960) andSisakyan et al. (1963). Ribosome from spinach were investigated byLyttleton (1962) andMurakami (1963) and fromClivia byMikulská et al. (1962). As part of a wider study of the mechanism of biosynthesis of nucleic acids in apple trees, we isolated ribosomes from the young green fruit and studied them by means of electron microscopy. Young apples were selected because cell division is very intense at this stage of growth of the apple.

Decreasing the illumination intensity of winter and semi-winter varieties of wheat to below a certain limit led to an accelerated development of the shoot apex of the main axis, whereas the development of spring varieties was slowed down. In plants whose development was accelerated by decreasing illumination intensity, the dry weight of the overground parts was smaller and the carbohydrate content of the shoot apex of the main axis was greater than in control plants growing under normal conditions of illumination. Plants subjected to long vernalization developed more rapidly and the weight of the overground parts was less than in plants subjected to vernalization for the normal time. The accelerating effect of decreased illumination intensity on plant development is explained by a changed manner of growth which is connected with a greater flow of assimilates to the shoot apex.

Quantitative determination of chlorophyll a and β can be made by paper chromatography of acetone extracts of plant material with colorimetric measurement of the eluates from the separated zones.
From the suitable solvent systems which give adequate separation of the pigments at a distance of 20 cm. from the start,Hager's mixture (1955) separates the chlorophylls better than the toluene-isopropanol (400: 1 v/v.) mixture, which, however, is better for the separation of carotenoids. Twice the amount of chlorophyll is separated on Whatman 31 ET paper, equally well and with the same time of development, as on Whatman No. 3 paper, on which it is possible to separate a maximum of about 15 μg of chlorophyll pigments per 1 em. start length. Losses on elution are, however, higher on using Whatman 31 ET paper. In plants with a high chlorophyllase activity, the error of determining chlorophyll a andb is greatly reduced if the leaves are placed for 1 min. in boiling water before extraction. For elution of chlorophylla andb from paper it is better to use anhydrous acetone, for chlorophyllides 80% acetone.
A comparison of the procedure investigated with the method of two-wave length spectrophotometric measurement of crude acetone extracts showed that in view of the average 10% loss, the chromatographic method is hardly suitable for determining the absolute amounts of chlorophylla andb, although the relation (a/b) can be determined with similar precision by both methods. Moreover, in view of the greater amount of work involved the chromatographic method can only be recommended for confirming the results of spectrophotometrie determination. Quantitative determination of chlorophylls from the area of the spot or from the "R_F" value can only be of an informative character.

Parallel measurements of the osmotic pressure (cryoscopic method) and the refractive index of cell sap were carried out on 246 samples from seven plant species. At the same time both values were ascertained as well as their relation for aqueous solutions of some sugars, organic acids and inorganic salts. The relations found with these model solutions are different for different substances. The quantitative composition of osmotically active components of cell sap changes in the course of ontogenesis and as a result the relation of refractive index and osmotic pressure also changes. By this comparison it has been shown that a reliable and more or less linear relation of the two values, which is advantageous for practical application, is only valid for a limited period in the ontogenesis of the experimental plant. The determination of the osmotic pressure of cell sap from the refractive index, the main advantage of which is its quickness and the small volume of sap required (0-02 ml.), is reliable if we construct empiricallyad hoc the appropriate correlation graph for the experimental plant for a limited ontogenetic period.

A description is presented of the principle of the method of increasing titres of antisera against phytopathogenic viruses, mycoses and bacterioses by immunizing with a precipitate-antigen according toDunin (1958). To a substrate containing viruses, bacteria or fungus spores, corresponding homologous antiserum prepared in advance is added to obtain a precipitate which is centrifuged and suspended in a small amount of physiological saline; this suspension (the precipitate-antigen) is used for immunization.
The method was used for the preparation of some diagnostic antisera of plant virus diseases and bacterioses. Thus, the antiserum against yellows in sugar beet (Beta virus 4) had its titre increased eight times as long as fresh juice was used for work. However, it was not possible to increase the titre if glycerol-preserved juice was used.
In preparing the antiserum againstPseudomonas lachrymans Sm. etBr., immunization by means of the precipitate-antigen brought about four-fold increase in serum titre as compared with the serum prepared in the usual way.
Antisera against tobacco-mosaic virus prepared by using the precipitate-antigen possessed a four times higher titre.
The above method was successfully used to prepare an antiserum against the potato virus from potato tuber juice containing the potato X virus. The titre, however, was lower than in the serum prepared from tobacco leaves infected with the X virus.
In preparing antisera against yellows in sugar beet (Beta virus X) from the juice of the beet root by means of the precipitate-antigen immunization, the sera did not react either with the juice from the roots or with that from the leaves of virus infected sugar beet.

It was shown that in the horse bean seeds (Vicia faba) the cotyledon proteins are identical, from an immunochemical standpoint, with those coming from the extracotyledon parts (radicle, young stem and embryonal leaves, in totality). However, the beginning of the germinative process exerts a different influence on the antigenic properties of the constitutive parts of the seed. The modification of the antigenic structure in cotyledons takes place slowly. On the contrary, in the extracotyledon parts a rapid decrease was found of the number of antigens present in the non-germinated seed. As the organs become differentiated, the hydrolysis process of these antigens goes on until their almost complete exhaustion. However, it appears that three of the initial antigens remain in the newly arisen leaves. Besides these antigens there are also specific-organ antigens which appear as the respective organs become morphologically differentiated. It was found that in the growing leaves the process of photosynthesis induces the synthesis of antigens characteristic for the mature leaves. The organ-specific antigens occur during plant development at the time when the leaf attains the morphological structure and the functional specialization characteristic for maturity.

This work is an examination of the possibilities of the application of microchemical iodine reactions in mycology, of their importance in phylogenesis, and of their practical application for the distinguishing of fungi or moulds from the tissue of the host plant. The best results were obtained with the reaction of chlor-zinc-iodine, then with chlor-calcium-iodine, and with iodophosphoric acid. Reactions were tested with different representatives of developmental groups of fungi and with pure cellulose (cotton-plant fibres) for the comparison of the quantity of cellulose, chitin, or of other substances in the cell-walls. BesidesOomycetes, whose cell-wall consists of cellulose, signs of a "cellulose" reaction appear also inZygomycetes. The species of the orderProtomycetales show a cellulose reaction, which fact also speaks rather for the ranking of this group in the division ofOomycetes. However, the microchemical reaction should not be overestimated, as its colour degree and intensity are influenced by the age of the mycelium of the fungi, by the thickness and physical properties of the cell-wall, and by the presence or absence of the cellular content.

Cyanus segetum LAM. was transferred from a long to a short photoperiodic regime at various stages of ontogenesis and the development of the plant investigated. The morphology of the leaves ofCyanus segetum was dependent on the photoperiodic regime. On a short photoperiodic regime, pinnately sected leaves were formed, but only if development was inhibited while the shoot apex still had a structure characteristic for the vegetative plant. The ability to influence the shape of the leaves by a short day ends before the morphological differentiation of the inflorescence at the time of the disappearance of the vegetative structure and the formation of the meristematic mantle. After this time all leaves were smooth-edged like those of the controls on a long day. Although the ability to influence leaves was limited to the period of initiation of the leaf primordia, it was not restricted to the primordia then being initiated. The conditions of development also affected leaves whose primordia had already been initiated. This was evidently due to the action of photoperiodic conditions via ontogenesis. The position of the axils was also changed in dependence on the photoperiodic regime.

An investigation was made of the anatomical structure of the shoot apex ofSenecio vulgaris L. a photoperiodically neutral plant, and compared with the formation of successive leaf primordia along the axis up to the initiation of the terminal inflorescence. In the shoot apex of a germinating plant a central zone can first be distinguished from the peripheral zone which is composed of small and intensely stained cells. Later, a rib meristem appears. At the time of the initiation of the middle (the largest) leaves, the shoot apex has a distinct small central zone and a well developed peripheral zone and rib meristem. Between these zones there is a group of cells dividing in all directions, the subcentral zone. At the time of initiation of the last leaves, the central zone extends to the flanks and gradually ceases to be distinguishable. At the same time, the subcentral zone increases in size. This is caused first by cell division and later, with the initiation of the last, most reduced leaves, by enlargement of the cells. Vacuolization in the inner part of the apex and the arrangement of the superficial cells in rows parallel to the surface of the apex, is a preparatory step to the initiation of the inflorescence.

Experimental investigations on the course of yellows-type virus infections in plantsTrifolium repens L. gave the following results:
During 24 and 48 hours after the completion of the test feeding period the clover phyllody and clover dwarf viruses spread in the plant maximally up to 5 cm. from the point of inoculation.
In the infected plants, the reproduced clover phyllody and clover dwarf viruses appeared on the average 5-6 days earlier than disease symptoms.
Acquisition feeding of leafhoppers onT. repens plants infected with the clover dwarf virus for different periods of time, revealed a decline in the virus concentration in the plants after 45 days from the appearance of disease symptoms. In plants infected with the parastolbur virus, this decline was not found.

1. A method of "measuring strips" for the investigation of the sap exudation of crops under field conditions is described. The quantity of liquid exuded from the detopped stem stump is determined from the length of a wetted zone of a narrow strip of filter paper protected against evaporation of the liquid by a polyethylene cover bag. The strips with the cover bags can be used even to collect greater amounts of exudated liquid.
2. Using this method, the sap exudation of detopped maize plants was observed during the whole growing season. On typical curves illustrating the course of the wetting of the measuring strips, the temporary absorption of the sap from the cells and conducting elements severed by the cut, the lag in exudation and the actual sap exudation can be distinguished.
3. The length of the lag period indicates the magnitude of the momentary water deficit of the investigated plant and the rate of sap exudation indicates the availability of soil moisture.
4. The rate of sap exudation reached its maximum at the end of June and then decreased gradually. In this period also the distinct lag periods were first observed. The occurence of shorter lag periods between the 5th and 29th July, i.e. in the shooting stage which from the standpoint of precipitation is critical for the height of yield, signifies that the critical stage probably coincides with the period in which the natural disproportion between available soil moisture and transpiration may become important.
5. During the period of long lags towards the end of the growing season, the measuring strips were fastened upon the plant stumps 24 hours after the decapitation. The "exudation after 24 hours" determined in this way indicates a significant decrease at the end of August when the soil moisture dropped to a value approaching the permanent wilting percentage.
6. The results have shown that the method of "measuring strips" permits an easy and sensitive evaluation of the water relations of maize plants growing under field conditions.

Decapitated seedlings ofLinum andPisum treated with TIBA paste either above or below the cotyledons, showed different morphogenetic changes especially on the epicotyl stumps, due to the differences in the correlations of their epigeous and hypogeous cotyledons respectively, these being also primarily responsible for the differing dominance of their shoot primordia.
At the earliest phases of germination, an antagonism between TIBA and IAA can be demonstrated on the first internode inLinum, which is usually very short, as well as on the petioles of thePisum cotyledons. The former could be enlarged only by treatingLinum seeds, even when ripening on the plant, with TIBA paste and the latter, if retained by soaking seeds ofPisum in a TIBA solution could be promoted by exogenous IAA. This, on the contrary, reversed the morphogenetic effects of TIBA uponLinum seeds.

Transpiration rates of leaf blades of irrigated and not irrigated spring wheat plants were studied in relation to the water content and growth changes in the test plants during their development. The applied irrigation stimulated the growth and slightly delayed the development of the test plants. It increased chiefly the water content and to a lesser degree the dry solid weight in the plant body. The quantitative and qualitative properties of the water content in the plant affected not only transpiration rates, but also the development of new and the dying off of old organs and tissues, especially of leaf blades. Transpiration rates in irrigated plants were markedly higher than in not irrigated plants. Mean transpiration rates of different leaf blades varied and were typical for each leaf blade. From the static aspect it was possible to express and even to explain some of the relationships and the heterogenity of the leaf blades on the same stem by the "Law of Zalensky". This involved mainly the mean values of growth characteristics and the investigated features of the water regime. On the other hand, from the dynamic viewpoint it was possible to divide the different leaf blades according to their transpiration changes into two groups. The first group includes the blades of the first to third leaf, the second group the blades of the fourth to sixth leaf and the ear. The capacity to control the water regime in the different blades is greatest at the stage of tillering, shooting and milk ripeness. During these developmental stages the marked decrease in transpiration, caused in the first place by a number of internal and not only external factors, was explained.