A simple modification of a laboratory gravimetric technique for the study of transpiration of intact plants is described, by which the process can be followed continually. The plants are grown in light vessels on a light "keramzite" or other suitable medium, either alone or in combination with agar gel. The mineral component provides for the necessary cultivation properties of the medium, whereas agar gel ensures steady and undisturbed water relations in longer experiments.
The calculation of the transpiration intensity per unite of time is described. For reliable results the number of samples must be lange chough, so that the coefficient of variation does exceed 10 per cent. The determination of the transpiration is sufficiently exact even without a correction for changes in dry solids, the absolute increments in dry solids during the time interval studied being of a smaller order of magnitude than the values of transpiration. The results are expressed per fresh weight of the transpiring unite, by which an undisturbed transpiration study of a longer duration is rendered possible and the effects on the plant are excluded.

In the pea test a highly positive response to the treatment with IAA reversed to a negative one or became 5 to 6 times weaker when CCC was applied together with IAA. In cultivating pea seedlings, following their decapitation, for two days in a 0.25 per cent CCC solution and then in water, growth of their cotyledonous axillaries (cotylaries) were inhibited. This inhibitive action of CCC could be made ineffective when the seedlings, following two-days' cultivation in the CCC solution, were grown further in kinetin solutions (0.37-3 mg per 1). Cotylaries of decapitated pea seedlings, when grown in kinetin solutions were inhibited. With kinetin solutions of 6-12 mg/l a strong inhibition also occured in the growth of roots at the apical parts of which spherical swellings were developing.
The CCC supplied to the roots of intact etiolated pea seedlings is translocated acropetally into the stem at a rate of about 5 cm per hour. Decapitation of the plant causes retardation of this transport, yet a coat of 0.00001-1% IAA or kinetin paste produces acceleration of the stream.
Existence of an antagonism between CCC and IAA, demonstrated earlier, was found holding true also for B-9 (N, N-dimethyl-aminesuccinamic acid) and IAA, as the inhibitive action of B-9, 0.06% solution on the growth of lettuce hypocotyls was reduced to a highly significant degree when the plants were supplied with B-9 together with IAA at a concentration of 10 mg/l.

We compared the occurrence of peroxidase isozymes in protein extract from roots, hypocotyls and cotyledons of 10 dayCucurbita pepo plants and of adult leaves of older plants by means of starch gel and polyacryl amide gel electrophoresis. We reached maximum discrimination by means of starch gel electrophoresis: 11 zones were ascertained on the cathode side and about 2 on the anode side at pH 3.1. Two zones occurred regularly:A and (the latter having a more complicated structure). ZoneD is characteristic for roots, but is it suppressed and seldom found with leaves. On the other hand zonesC ₁ andC ₂ are clearly discernible with leaves but are substantially less evident with roots. The character of anodic zoneZ is discussed later in this paper.

Development of the shoot apex up to floral differentiation was investigated in the short-day plantChenopodium rubrum. The changes occurring in the apex from energence until full opening of the cotyledons (Figs 1-4), development during photoperiodic induction (Figs. 5-8), as well as the resulting floral differentiation (Figs. 9-10) are described. It was aimed at excluding the influence of plastochron changes on the interpretation of ontogeny of the shoot apex. For that reason two planes of longitudinal sections and two plastochron stages were compared.
In young plants zonation does not become fully evident prior to floral differentiation. The anatomical structure of the shoot apex does not change substantially during the first two inductive cycles which proved to be obligatory under the given experimental conditions. The changes occurring during two further inductive cycles correspond to the total activation of the meristems as manifested by the growth and branching of the apex preceeding floral differentiation proper.

Experiments were conducted to compare the efficiency of transmission of a strain of pea mosaic virus (PMV) isolated in Czechoslovakia by two strains (clones) of the pea aphidAcyrthosiphon pisum Harris (green and red) and one strain ofMyzus persicae Sulz. PMV is a nonpersistent virus and the preliminary fasting of aphids before acquisition feeding increases the efficiency of aphids in transmission of this virus. In our experiments two hour fasted individuals were used and two periods of acquisition feeding on the source (1 and 5 minutes). On the healthy test plants the aphids were left over night. As the source and test plants pea (Pisum sativum L.) of the cv. Raman were used. During the one minute acquisition period on the source of infection the aphids were observed under the stereoscopic microscope. They usually made two to three probes. During the five minute acquisition feeding time the aphids were not observed and they were taken from the source of infection after a lapse of five minutes. To compare the efficiency in transmission of this virus by these aphids only one aphid per tested plant was used and in all trials only two to four day old nymphs were taken. Differences in transmission efficiency between two strains ofAcyrthosiphon pisum Harris were highly significant. The green strain of pea aphid was the less efficient vector in comparison with the green peach aphid and the red strain of the pea aphid, the latter being the most efficient vector of this virus.

The exodermis of ash roots is initiated early in the apical meristem. When fully differentiated, it is composed of alternating "long" and "short" cells measuring approx. 70×25×25 μm and 25×28×25 μm respectively. At a short distance from the apex, the long cells undergo structural and histochemical changes from a "primary" towards a "secondary" stage: an impermeable suberized lamella is formed, cellulose lamellae become impregnated by lignin, and the protoplast dies off. The short cells show a distinctly thickened outer wall ("cap") which is composed exclusively of cellulose, and possess abundant cytoplasm with a large nucleus. In the process of ageing the structure of short cells is not markedly affected. Following the early disintegration of rhizodermis, the exodermis works as the external protective layer of tho fragile end-root. Its long cells fulfil the mechanical protection, the short cells serve as passage cells for solutions and gases, during the whole life-span of the rootlet.

In the experiment with 18 winter varieties the genotypic, phenotypic and environmental correlations were estimated in all combinations between the pairs of 11 quantitative characters.
Both yield of grain with its components and further characters were evaluated, of which flag leaf size and leaf angle of the last but one leaf are of importance for the utilization of light energy and consequently for receiving maximum rates of photosynthesis.
In simple genotypic and phenotypic correlations their different stability with regard to mineral nutrition, eventually to the date of sowing was proved.
In the discussion the limited signification of simple correlation for the statement of complicated processes in plants caused by multiplied associations of characters was pointed out. In the example of yield components of the plant at the application of 60 kg N per hectare it was shown that also further unknown variable factors might participate in the genotypic correlation. It may be concluded that the inclusion of them when constructing the selection indexes will give further foundations for handling yield as a breeding or genetic character, and for the causal analysis of yield formation in wheat.

When small branches of different plants were dipped after cutting into a solution of humic acid, a brown substance penetrated into vessels and coagulated there. The vascular bundles were stained to the height of 1-6 cm after a week. The presence of the humic acid in the parenchymal cells could not be demonstrated directly, but cells with a yellow or brown cell wall remained alive (they could be plasmolysed).
Humic acid, labelled with C¹⁴ was distributed in the same way in sterile and in non-sterile plant cultures, mainly through vascular bundles.

The biological effect of barley root excretions was studied during a 4 to 10 days cultivation period. The effect of root excretions changes according to the cultivation period of barley. It was ascertained by means of a bioassay that growth was either conclusively stimulated or the root excretions did not affect growth of the roots and of the upper part ofNasturtium. No significant inhibitory effect was observed. The effect of the single amino acids and of their mixtures found in the root excretions of barley was quite different. The following amino acids were determined by paper chromatography in root excretions: alanine, asparagine, phenylalanine, glycine, leucine, lysine, serine, tyrosine, glutamic acid and valine plus methionine. During cultivation their total quantity increased from 5.48. 10^-5 up to 1.13. 10^-3 mg per plant. Most of the 20 amino acids observed, displayed in theNasturtium test at a concentration from 0.1 to 1,000 mg/l an inhibitory effect onNasturtium growth. The effect of amino acid mixtures, corresponding qualitatively and quantitatively to the free amino acids in barley root excretions was dependent on their concentration.
Growth regulators of the auxin type were found in culture solutions by chromatographic separation and with bioassay. As it may be seen from the results obtained, there are besides amino acids and indole derivatives other non-identified compounds involved in the effect of barley root excretions.

Dispersing of splits of NaCl and KCl during the drying process has been found using labelled²⁴Na and⁴²K preparations. This bursting effect can cause some misinterpretations in biological experiments with plant material.

A gasometric method was developed for measuring water deficit in leaves. For a leaf at full turgor the amount of water penetrating into the tissue after removing the air from intercellular spaces by means of a vacuum pump, is equal in volume to the gas removed from the intercellular spaces. In a leaf with a water deficit the amount of the infiltrating water is greater than the removed gas volume by the amount egual to the water deficit. Determination of the volumes of the gas removed and penetrating water enables water deficit, if any, to be calculated. Comparative measurements carried out on five plant species confirmed the correctness of the method suggested. Reduction of the measuring time allowed to eliminate completely the sources of errors associated with the growth of tissue and loss of dry weight during respiration.

In estimating the water-holding power and thus also their drought resistance, the portion of curvature as shown by the desiccation curves (transpiration, loss curves) appears most suitable in which the water-binding forces within a plant body feature a steep and characteristic rise. Since this portion of the curving stage coincides, in the majority of cases, also with the linear stage for the desiccation curves as described byCetl, this author's method of establishing drought resistance of plants (Cetl, 1953, 1957) may be applied to good advantage also to the woody species seedlings. For particularly urgent instances serving the purpose of orientation a modification of this method has been suggested, as follows: following cutting off the seedling the output of water is weighed at these intervals only: 0, 60, 120, and 240 minutes; as the criterion for drought sistance the resulting value for the rate of water output (v) is taken as measured between the interval of 60 and 120 minutes. When a detailed analysis is made it is advisable to consider the v value measured for the interval between 0 and 60 minutes and for that between 120 and 240 minutes. Moreover, it is likewise advisable to maintain the soil with experimental seedlings at the level of optimum moisture (60 to 80 per cent maximum capillary water capacity), for some 18 to 22 hours prior to the seedling's abscission.

The effect of 2-thiouracil on vegetative growth and floral differentiation was investigated inChenopodium rubrum plants grown in water cultures. Between the low concentrations of the agent, stimulating vegetative growth and floral differentiation, and those inhibiting both these processes, a narrow concentration range was found (1.10^-5 m to 2.10^-5 m), where growth was inhibited selectively. At a concentration of 1.10^-4 m a selective inhibition of development was found when 2-thiouracil was applied at the beginning of photoperiodic induction. Inhibition of development was strong regardless of whether 2-thiouracil was applied before, during or closely after 4 days of photoperiodic induction; the degree of growth inhibition, however, changed in dependence on photoperiodic induction. The strongest relative inhibition of development, calculated as a ratio between development and growth, was observed always at the beginning of photoperiodic induction.
Investigation of plant growth as well as the anatomical and autoradiographic study after the application of 2-thiouracil indicate that the inhibition becomes evident at the end of 4 days of application by an overall growth inhibition and a decrease of mitotic activity. Reversal by uracil was possible after simultaneous application of 2-thiouracil. The nature of the selective inhibition is discussed and two possible interpretations of the data obtained are analyzed: a) different response of growth processes in apices and young vegetative organs respectively with regard to different participation of cell division and elongation, b) specific inhibition of floral differentiation.

The differentiation of tissues is closely connected with the proteosynthesis. One can therfore assume that tissues with different types of cell growth (meristematic or elongation growth) and with different degrees of differentiation are different in their protein composition. In order to compare the protein composition of different plant organs, the method of disc electrophoresis on a polyacrylamide gel has been used by some authors. As compared with other methods used up to now, e. g. isolating proteins on DEAE cellulose or in Sephadex, this method does not need so much material and its resolution ability seems to be higher. It is also quicker and enables the study of several samples simultaneously. Its disadvantage is that proteins can be identified mainly by means of Rf and their quantity, measured from the intensity of staining of individual fractions in the gel, which may be misleading due to different sorption capacity of different proteins (FričFričová 1967). None the less, it is good for comparison of protein composition of individual parts of the plant body.
Different methods have been used to compare protein composition of individual growth zones in roots.Barsky,Ivanov andPushakova (1965) used luminiscence microscopy and found that in maize roots it is not possible to find substantial differences by this method.Morgan andReith (1954) arrived at similar conclusions. On the other hand,Steward et al. (1965) andMorris (1966) found qualitative differences in protein composition of different parts of pea roots using acrylamide electrophoresis. The results of the last named authors show considerable discrepancies in details, due perhaps to a different method of extraction (buffer, pH, purifying method).
We have used acrylamide gel electrophoresis for investigating proteins in precisely defined growth zones of theVicia faba root.

The author of this paper has attempted to clarify some problems concerning the nomenclature of Golgi apparatus and Golgi zone. The actual aim of this paper is to summarize - while using the more safe nomenclature-the existing knowledge about the functional relations between nucleus and cytoplasm arising from the study of the juxtanuclear zone by electron microscopy. Some observations lead to the assumption that the juxtanuclear zone is the place where cell components are formed or transformed. Considering its temporary character in proliferating cells and taking into account the connections with endoplasmic reticulum and the presence of pores, the nuclear membrane remains apparently a barrier restraining the spontaneous movement of substances and of cell components respectively between cytoplasm and karyoplasm that can be seen e.g. in the grouping of cytoplasmic formations in the juxtanuclear zone. In plant cells, within the zone mentioned agglomerations of different cell formations have been found, either the Golgi apparatus or mitochondria, secretion granules, lipid inclusions, vacuoles or plastids. Such a gathering of cytoplasmic material has been observed especially in young embryonic cells or in cells with retarded or stopped metabolism. The older and/or intensively active cells would then absolve an expansion of the cytoplasmic material into the whole cell. Similar formative mechanisms, now available for study during some ontogenic phases or at definite functional states only, could be effective even in the course of phylogenesis. From this point of view some of the formations described could be regarded as a kind of atavisms.

When the lethal radiomutant chlorina 42 was cultivated on glucose containing and glucose-free medium the cotyledons of the matant sown on glucose medium had a higher chlorophyll content than those of the matant sown on glucose-free madium. In further cultivation of this mitant on glucose medium until flowering the total chlorophyll content is maintained at the same level, it increases slightly in the case of flowering plants. The mutant cultivated on glucose medium differs somewhat with regard to the content of free amino acids from the green control cultivated also on glucose medium over the whole vegetation period. The former has a higher glutamine content than the latter and in some growth phases also a higher content of asparagine. It is assumed that the insufficient photosynthetic activity is apparently not fully compensated by glucose and the plant has to supplement its energy balance by partial oxidative protein catabolism even under the conditions of artificial nutrition.

The liberation of phosphoric acid from glucose-1-phosphate, catalyzed by phosphorylase was studied in wheat growing in sand cultures with an addition of humic acid and hymatomelanic acid. It was found that the phosphorylase activity of tissues changes under the influence of humic acid very significantly. The maximum activity is reached at 10 mg humic acid/liter. The overground organs are less sensitive, as a stimulation effect is reached there only at 400 mg/liter. The effect of hymatomelanic acid is negligible in comparison with that of humic acid. The observed phenomenon is related to the effect of humus substances on the equilibrium of saccharides and on the distribution of dry matter in the plant.

1. The differences in the dynamics of the origin and further development of the water saturation deficit (WSD) in leaves of different age from 100- to 120-day-old plants of fodder cabbage and rape were investigated.
2. WSD in leaves of different age detached from plants and wilting without water supply develops most quickly in young and most slowly in old leaves. This is in basic agreement with differences in transpiration rate.
3. When entire plants are cut off, leaves of different age wilt at the same rate. In the later phases of wilting, (i.e. at a WSD value of over 20 to 30%) slightly higher WSD values were found in old leaves.
4. During slow wilting of plantsin situ, induced by decreasing soil moisture, a definite preference of young leaves in water supply was determined commencing from medium WSD values, i.e. on an average from 8 to 20%. During total lack of water in the plant, old and adult leaves wilt markedly and die off; the WSD of young leaves remains for a long time at comparatively low values.
5. In the observed preference of young leaves, the translocation of water to young leaves from the wilting older leaves takes a part.

Metabolic disturbances inNicotiana glauca, a symptomless carrier of potato witches' broom were studied. The dry weight content of leaves of diseased plants was slightly decreased, that of the stems increased. The ash content in the dry weight of the whole diseased plant was decreased by 11%. Contrary to tomato plants which had shown considerable disproportions in the distribution of metabolites among the individual organs investigated (ULRYCHOVÁ, LIMBERK 1964), the content of the total nitrogen and of the individual nitrogen fractions of both leaves and stems of diseasedNicotiana glauca were decreased. The content of glutamine was increased in both organs in spite of the decrease of ammonia nitrogen by nearly 30% in both cases. The most striking disturbance found in the diseased plants ofNicotiana glauca was the 67% increase of a low-molecular phosphorus fraction (P extractable with 0-2N HCIO₄) in the leaves. This result agrees with that found in diseased tomato plants and may be primarily associated with the virus infection. The content of all other phosphorus fractions of both leaves and stems was decreased.

Two techniques recently described for the demonstration of protein SH in animal material were appllied to plant objects in this work: the technique with β-oxynaphthylmercurichloride and that with p-nitrobromacetophenone. These techniques together with DDD¹ and RSR¹ usually produced more intense staining in plant cell nuclei than in the cytoplasm. When reactions for protein carboxyls and tyrosine were used, similar differences in the intensity of staining the nuclei and cytoplasm were observed. It appears that the differences in the intensity of reactions for protein SH groups correspond to the differences in the concentration of total protein in plant meristematic cell nuclei and cytoplasm.

The cytological analysis of 25 Yugoslav rye populations, collected from Slovenia Serbia and Macedonia, showed the presence of B chromosomes in the all populations analysed (100%). The number of B chromosomes present was small, from 1 to 3, while the average number per plant ranged from 0-13 to 0.97. The frequency of rye plants with B chromosomes for Yugoslavia had an average of 27.10%. The frequency of plants with B chromosomes and the average number of that chromosome category per plant were appreciably greater in the arid region of Macedonia than in the humid region of Slovenia, the differences being significant and real biometrically.
Comparing the data of other authors for primitive Asian rye populations, it was established that the B chromosome frequency is lowest in the populations from regions designed as centres of the origin of this plant species (Near East, Asia Minor), with a considerable successive increase of their frequency further as well toward the East (Transbaikal, Korea), as toward the West (Balkan Peninsula, Yugoslavia). Possible causes of the B chromosome frequency increase in the populations out of the centres of rye origin were discussed, and it was pointed out to the importance of their study in primitive West European populations.

The enzymatic transamination reactions between aspartic and α-ketoglutaric acid and between aspartic and pyruvic acid were studied in fresh dialysed extracts of young wheat plants cultivated under various trophical conditions, in mineral solution (Knop), in the solution of an soil organic substance (potassium humate) and without nutrients (H₂O). Simultaneously, the level of endogenic aspartic acid, glutamic acid and the growth values were determined. The enzymatic reactions were characterized by determining the optimum pH, the time course, and the effect of coenzyme and of inhibitors.
The activity of the aspartate-glutamate transaminase from the root system of plants was considerably higher than the activity of the overground organs. The enzymatic activity from both parts of the plant was inversely proportional to the growth rate: intensive growth of the plants from the Knop variant was connected with their low enzymatic activity; the level of endogenic glutamic acid was high. The slow growth of the plants without nutrients was connected with a higher enzymatic activity; the level of endogenic glutamic acid was low. The plants from the potassium humate variant had an intermediate position between these two variants from the point of view of growth as well as from that of enzymatic activity. The plants with insufficient nutrition (slow growth, low level of endogenic glutamic acid) apparently have a low capacity for supplementing the glutamic acid deficit, which is essential for the metabolic processes, by increasing the activity of the reactions leading to glutamic acid synthesis (Asp-Glu) and, on the other hand, by decreasing the reactions utilizing it (Glu-Ala). For wheat plants the active aspartate-glutamate reaction is obviously physiologically more important than the direct reaction glutamate-aspartate and the reaction aspartate-alanine which in all cases had a very low activity.

Papaver somniferum plants grown in pots in the phase of forming the first pair of leaves were treated by 6-4 ml of 0-02% solution of 3-amino-l,2,4-triazol (amitrol) per single pot, which is equal to the dose of 2 mg of amitrol per 100 cm² soil area One, four, seven and ten days after the application the effect of the herbicide on some physiological processes in the overground organs of plants was investigated.
Amitrol decreased the activity of catalase by 60% compared with control plants 1 day after the application, even though no external symptoms of damage were evident. On further action, the activity of catalase was suppressed somewhat less. The respiration was not inhibited by amitrol to such an extent as the activity of catalase. One day after the application the respiration was not suppressed significantly, at further dates the respiration activity decreased. The difference between the respiration of treated and control poppy plants was particularly evident when the oxygen consumption was referred to a single plant. Under these experimental conditions we failed to determine the activity of ascorbinoxidase and peroxidase. The activity of polyphenoloxidase was stimulated by amitrol from the fourth day after the treatment.
On the basis of these experiments we can say that poppy has not a physiologically based resistance to amitrol.

Labelled carbon dioxide was supplied for 22 hrs to a leaf of the leader or to the lateral shoot in two-year-old apple seedlings. The distribution of radioactive assimilates within the plant following this treatment was investigated by using radioautography.
The transport of labelled assimilates from the young leaf of the leader was very meagre and affected only parts of the stem and the leaves situated in the close vicinity of the treated leaf.
The¹⁴C-labelled assimilates from the mature leaf of the leader were transported in a considerable amount to the apex and to the other leaves of the leader. They were also found in an appreciable amount in the stem and the roots, as well as in some lateral shoots.
After supplying¹⁴CO₂ to the lateral shoot remarkable transport of labelled assimilates was observed. Radioactivity was detected in the tip and in the youngest leaves of the leader, as well as in the roots. Their path in the stem was studied by dissecting the plant and examining the cross section from each internode. This method revealed that the assimilates from the treated leaf or shoot were transported downward only on one side of the stem in a helical pattern. The lateral shoots situated on the radioactive side of the stem were also labelled, whereas those situated on the opposite (non-radioactive) side were not labelled.

The cotyledonary petioles inPisum sativum developing at the start of germination, as well as the cotylaries growing out after decapitation of thePisuin seedlings manifest very often the so-called lateral correlations, since one of them suppresses the opposite primordium when the growth inhibition in the plant coinciding apparently with the growth promotion results necessarily in a normal development only of one of these originally equal primordia. These correlations also seem to be mediated by auxin, being induced by gravity or by corresponding cotyledon and root products, which can be supported by the use of exogenous auxins.

The suction force of active roots ofFraxinus excelsior L. was estimated by the refractometric compensation method (compensation in a sucrose solution) and its dependence on the water content of soil was determined. Where differences in the soil humidity were excluded within the root system, the dependence could be expressed by a curve resembling the dependence of the suction force of soil on its water content. This dependence was valid both for the minimal gradients of suction forces between the over-and underground parts of the plant (pot experiments), as well as when transpiration and hence gradients were present (under field conditions). Where differences in soil humidity were formed within the root system, the dependence did not correspond to this basic curve, due to the compensation of root suction forces within the root system.

Pea seeds were subjected to 1; 5 and 20 krad doses of⁶⁰Co γ-raýs. The irradiated seeds were planted in damp sand and in Petri vessels. After 10-daý vegetation at room temperature and under natural light conditions the content of the following components was determined in ýoung plants: free thiamine and thiamine pýrophosphate and drý substance.
It was found that 1 krad dose stimulates the growth of the plant and increases the crop of its green parts. The doses within the range of 1-5 krads do not affect the production of thiamine. The content of the latter, particularlý in its free form, increases markedlý for the dose of 20 krads. However, such doses hamper the vegetation.
In conclusion it seems that doses of the order of 1 krad lead to positive results in respect to the growth of the plants, however, neither thiamine biosýnthesis nor its phosphorýlation is stimulated under these conditions.

Changes in water uptake immediately following the application of high concentrations of 2-methyl-4-chlorophenoxyacetic acid (MCPA) into the root medium of whole plants ofPisum sativum andVicia faba were investigated potometrically under controlled conditions. It was found that concentrations between 10^-2 and 10^-5 m bring about a sudden, pronounced and lasting inhibition of water uptake. Its rate depends directly on MCPA concentration. At 10^-2 m, sudden inhibition of water uptake becomes apparent as early as 10 min after application. With decreasing concentrations the appearance of inhibition is retarded but the inhibition is still sudden and well-pronounced. The inhibition of water uptake observed after MCPA application to the root medium of whole plants agrees with the sudden striking reduction in transpiration intensity observed byAllerup (1964) after the application of similar concentrations of 2,4-dichlorophenoxyacetic acid. The presence of MCPA in the nutrient medium causes inhibition of water uptake even in cut plants. Its rate again depends on the concentration of the growth substance. The inhibition does not appear here as quickly and is not as sudden and pronounced. High concentrations of MCPA during application to over-ground plant organs do not bring about immediate inhibition of water uptake by the root.

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.