The paper deals with the effect of the application of certain ions (Zn²⁺, B₄O₇ ^2- Mn²⁺, Cu²⁺, MoO₄ ^2-,) on the development of the activity displayed by amylase, urease, and glutamate-oxalacetate (GOT) in hydroponically cultivated barley during the first seven days of ontogenesis. The enzymes were studied separately in the overground and root parts of the plants. The following main conclusions can be drawn from the findings made: The amylase activity of the control plants in connection with their development diminished slightly in the overground part, while it was relatively constant in the roots. Due to the effect of certain elements tested, this activity increased pronouncedly (significant differences were confirmed in variants containing MoO₄ ^2-, Zn²⁺, and Co²⁺). The urease level in the overground part of the control plants remained low throughout the entire experimental period and was only little influenced by the individual microelements under study (with the exception of B⁴O₇ ^2-). On the other hand, the urease activity in the root system increased markedly, the B₄O₇ ^2- ions exhibiting a significantly stimulating effect. The activity of glutamate-oxalacetate transaminase (GOT) in the overground part of the control plants increased only slightly in the course of the initial development, while in the root system it grew relatively more pronouncedly. In the overground part of the plants all the microelements administered displayed a significantly depressive effect on the development of this enzyme activity; in the roots, the inhibitory action was maintained only in the last experimental period in variants with Zn²⁺ ions.

Fluorescent tubes were found to be most suitable for the biological determination of gibberellic acid by the lettuce test method. On applying this type of illumination, the difference in hypocotyl length between the control and the experimental variant with GA 3 was greatest. The application of gibberellin to lettuce seedlings in darkness is by far not so marked as to those cultivated under any of the types of illumination used. Description of a Plexite chamber in which the lettuce seedlings arc tested is presented.

Experiments revealed that the synchronized cultures ofScenedesmus quadricauda, strainGreifswald/15, must be kept under continuous illumination throughout the whole growth phase (from the release of daughter coenobia up to the moment when all cells are capable of further reproduction). The length of the light period is among others the function of the suspension density. With regard to these facts a method of synchronization was worked out on the basis of a rhythmical repetition of the calculated light regime, corresponding to the physiological parameters of the synchronized strain under given cultivation conditions. This method enables to maintain synchronized cultures in adequate cycles for any required period, even in sufficiently dense, linearly growing suspensions. It may be applied to any chlorococcal algae; however, if coenobial types are studied, it is necessary to consider special peculiarities, which result from the regular arrangement of the cells in the coenobium.

The production of pectic enzymes byHelminthosporium atypicum and its morphogenesis on different media were studied. It was observed that the fungus produces pectic enzyme (macerating enzyme) adaptively. Increasing concentrations of glucose had an inhibitory effect on enzyme production. Glucose promotes profuse growth and early sporulation whereas presence of pectin slows down the growth and delays sporulation. Delay in sporulation is the effect of presence of pectin and not of the low pH of the medium. It is also suggested that in the case ofH. atypicum low pH of the medium does not allow the fungus to utilize a carbon source as efficiently as at higher pH.

2,4-D was applied to the roots of diploid and tetraploid corn. After the application the mitotic division in the meristem of root tips was blocked; the mitotic division in differentiated cells of cortex and central cylinder, on the other hand, was provoked. In the cortex of diploid corn (variety České) predominantly tetraploid were found cells with 28 chromosomes and, to a lesser extent, octoploid and diploid ones with 56 and 14 chromosomes respectively. In the cortex of tetraploid corn (variety Bernburger Tetraroggen), most cells were octoploid with 56 chromosomes; the metaphase levels with 112 and 28 chromosomes, e.g. 16-ploid and tetraploid cells, were found less frequently. The relations between the numbers of cells with different polyploidy were similar in both the varieties. The first endoreduplication cycle was different polyploidy were similar in both the varieties. The first endoreduplication cycle was found to occur in the region where the cortex cells finish their elongation. In the central cylinder of the roots of diploid corn most cells were found to be diploid, in tetraploid corn most cells were tetraploid.

An investigation was conducted to study the interrelation of free amino acid metabolism and root formation in etiolated pea stem sections as dependent on time and on inhibition of root formation by kinetin and ethionine.
The rise in the level of aspartic acid and increase in the rate of conversion of¹⁴C-labeled glucose to free amino acids were found to be characteristic features of the formation of foci of meristematic cells in pericyclo region. The formation of roots was reflected, in general, much more in the rate of conversion of labeled glucose to free amino acids than in the levels of corresponding amino acids.
The total amount of free amino acids was not significantly changed during incubation of stem sections in a solution of kinetin (5×10^-5 m). A rapid fall in their level was recorded in the next 24 hours. The incorporation of¹⁴C from glucose into a precursor of lignin, phenylalanine, was completely inhibited by kinetin which stimulated simultanously the growth of adjacent buds. Stimulation of secondary xylem formation, which appeared later, was accompanied by the resumption of¹⁴C-incorporation into phenylalanine.
Inhibition of root formation by ethionine resulted in the rapid fall of the level of most amino acids and in a significant decrease in the rate of incorporation of¹⁴C from glucose into amino acids. A decreasing level of ethionine in tissues during cultivation of ethionine-treated stem sections was accompanied by a gradual rise in the individual amino acids and in the rate of conversion of glucose into free amino acids.

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.

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.

The rate of growth of 5 species of white-rot fungi on an agar medium with additions of humus acids was used for assessing the ability of these fungi to utilize humus acids as a sole source of nutrition. Differences in the effect of the various fractions of humus acids and their concentrations, as well as in the reaction of the fungi tested were observed. During the growth, loss of colour of agar media with humus acids was observed. Activity of lacease in the discoloured areas was highest.

Floral differentiation ofChenopodium rubrum is more AD-sensitive than growth of the vegetative organs. With a suitable combination of the manner of application and the concentration of AD used, selective inhibition of flowering can be attained without any effect on growth. The inhibition of flowering was greatest if AD acted during the first two days of photoperiodic induction. With later application its effect on flowering was weaker. RNA synthesized in the first days of photoperiodic induction to a considerable extent ensured its further course.

In young pumpkin plants, the phosphorus was found not to be affected substantially by potassium deficiency whereas the deficiency of calcium has marked effects. Potassium distribution is not affected substantially by either phosphorus or calcium deficiency.
In short-term experiments, the presence of calcium affects markedly the total uptake of potassium but the potassium distribution remains unaltered. The stimulation of potassium uptake is far more pronounced in plants pre-cultivated in a complete nutrient solution than in those pre-cultivated in a calcium-deficient one; this is apparently due to profound metabolic changes taking place in plants grown without calcium.
The reserves of phosphorus and potassium stored in the cotyledons are easily mobilized and translocated so that they can be used for growth in early stages of development; the appearance of pathological symptoms of phosphorus or potassium deficiency is thus prevented.

The cryosestonic unicellular green algaKoliella tatrae (Kol) Hind., which grows in the surface layers of the summer snow-fields of the Vel'ký Žl'ab valley in the Belánske Tatry Mountains (Czechoslovakia), was started to be cultured at the laboratory. This alga may be considered as a typical (true) cryobiont, the optimal growth of which requires about 4°C; long-lasting temperatures ranging from more than 10°C have a lethal effect. The low-temperature strain obtained is suitable for the comparison with unicellular green algae, used as models for the study of the photosynthetic activity and metabolic processes of autotrophic micro-organisms (Chlorella, Scenedesmus, etc.).

Of twenty common oligosaccharides, monosaccharides and sugar alcohols tested, raffinose was found to be the best substrate for growth and respiration of apple pollen tubes. While in a solution of sucrose growth is retarded after about six hours, accompanied by a decrease in respiration intensity, no such decrease was observed in pollen tubes cultivated in a solution of raffinose even after 10 to 20 hrs. of growth. Raffinose is inverted by pollen tubes much more slowly than sucrose which is taken as the cause of the long-term effect of raffinose. Pollen did not germinate at all in a solution of turanose.
It thus appears to be probable that the primary factor in the specific effect of sucrose and raffinose on the growth of apple-tree pollen tubes is the presence of β-D-fructofuranose in the sugar molecule.

If both cotyledons are amputated from non-decapitated pea seedlings, the intensity of transport of³²P into intact epicotyls is raised more than twofold. This is apparently connected with the regulatory-inhibitory effect of the cotyledons that can be simulated by a 0.1% paste of indoleacetic acid (IAA). If both amputated cotyledons are replaced by this paste, the intensity of³²P transport is again decreased to the level found in plants with intact cotyledons.
When etiolated pea seedlings grown in the dark in 100% relative humidity were decapitated, the³²P transport to the top of the epicotyl stumps covered with 0.5% IAA paste was strikingly decreased if the stumps were covered below with a 10% paste containing chlorocholine chloride (CCC) or with a 0.5% paste containing triiodobenzoic acid (TIBA). On the other hand, the intensity of³²P transport was significantly increased if the IAA paste was put above a 0.5% paste with kinetin which alone does not raise the transport intensity. No such synergism toward³²P transport could be established between IAA and gibberellin.

Root formation in the etiolated pea stem sections and inhibition of this process is described in the present paper. Sodium fluoride, iodoacetic acid, norvaline, phenylserine, 5-bromuracil and 2-thiouracil did not inhibit the root formation completely. Complete inhibition, however, was observed after treatment of pea stem sections by kinetin, ethionine and chloramphenicol (5 X 10^-5 M, 1 x 10^-2 M, and 1 x 10^-2 16 hours after sectioning). The concentration of kinetin which produced complete inhibition of root formation simultaneously stimulated the growth of the lateral buds.
Root formation under the conditions described below can be divided into two stages. The first stage 64 hours from the beginning of the experiment, the second stage 64 hours later. Further, the first stage includes the formation of the meristematic cells in the pericycle areas. In the second stage are included the growth of roots and differentiation of root-tissues. Roots were formed, first of all, in the short vertical region of the sections near to the basal buds. Secondary xylem formation was also observed during the cultivation of the sections. This process was stimulated by kinetin.

The catabolism of specifically¹⁴C-labelled glucose during the root formation and its inhibition by kinetin and ethionine in the etiolated pea stem sections were studied. The formation of root meristematic foci in the pericycle region of sections was accompanied by the decrease of the C₆/C₁ ratio. Such a result and activation of pentose phosphate cycle, which was also checked by another method, suggested increased participation of pentose phosphate cycle in glucose oxidation. The above mentioned changes were also found after the prevention of root formation by ethionine and, therefore, do not seem to be specific for the meristematic foci formation. The growth of newly formed roots was closely connected with the rise of C₆/C₁ values.
The increase of CO₂ release from the first carbon atom of glucose molecule was recorded after the inhibition of root formation by ethionine.
The rise of C₆/C₁ values and decrease of pentose phosphate cycle activity was observed after the treatment of pea stem sections by kinetin in the first 64 hours after sectioning. In this case root formation was prevented and the growth of lateral buds was stimulated. The secondary xylem formation which took place later was accompanied by the activation of the pentose phosphate cycle. These phenomena are discussed in relation to cell division and biosynthesis of lignin-precursors.

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.

A method of calculation for determining the total transpiration (consumption of water for transpiration) of a single woody plant seedling or of their growth during periods of different length (from one day up to the whole vegetative season) is described and critically evaluated; the calculation is performed according to single transpiration intensity measuring results, by the cut-shoot method and weighing at 8, 11, 14 and 17 hours (or more often during the day).

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.

6-azauracil (AU) and 2-thiouracil (TU) were applied to the short-day plants Pharbitis Nil and Chenopodium rubrum and to the long-day plants Hyoscyamus niger, Lolium temulentum and Triticum aestivum cv. Chlumecká 12 at different times before, during or at the end of floral induction. In wheat the effect of 5-bromouracil, 5-iodouracil and 2-thio-6-azauracil was also tested.With the exception of bromouracil, which slightly stimulated flowering in wheat, all analogues either strongly inhibited or completely blocked flowering when applied in appropriate concentrations a short time prior to induction or at its beginning. Treatments given a longer time before induction or after its termination was less effective. Inhibition of flowering was always associated with damage to the vegetative growth. The effect of TU was reversed by uracil and that of AU by uridine, if these compounds were applied simultaneously with the analogue at a concentration exceeding at least 5 times that of the analogue. Reversal also applied to vegetative growth. Simultaneous application of gibberellin and analogues did not remove the inhibition.

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.

The effect of sowing density (21, 85, 340 and 3400 plants per 1 m on the leaf area index (LAI), vertical arrangement of developing foliage and dry matter production was investigated in stands of wheat (Triticum aestivum L. cv. Niva).
1. With increasing sowing density.
a) The LAI increased and the highest LAI = 9.6 was obtained with 3400 plants. m-2. The largest development of foliage took place at ear emergence with 85, 340 and 3400 plants. rn-2, and in the flowering phase with 21 plants. m-2.
b) The overal leaf area duration was reduced, with a difference of 11 days between the lowest and the highest density.
c) The number of leaves formed per one stem increased from 5 to 8.
2. An increase in theLAI affected the vertical distribution of leaf area and resulted in increased differenoes in relative light intensity between the top and bottom layers of the leaf canopy. Differences inLAI were linked with differences in leaf area duration and in the relative proportions of leaves of different age in the total number of leaves per 1₂
3. a) Shoot dry matter production increased with increasing density; the maximum of 3811 g. m_-2 was obtained with 3400 plants._M-2.
b) The dependence of grain yield on sowing density had a parabolic character; the maximum yields of 47001 g. m-2 and 442.8 g m-2 were obtained with 340 and 85 plants. respectively.
c) The optimum LAI for the formation of grain yield was 2.3 to 3.2.
d) The crop growth rate (C) increased with increasing density; the highest mean recorded C = 594 g. m. week-1 corresponded to LAI = 9.6.
4. Thinning the stands of 3400, 340 and 85 plants. m-2 in the phases of the 3rd leaf (22 days after sowing) and of tillering (30 days after sowing) to the next lower density resulted in a reduced LA leaf and tiller number, crop growth rate, shoot dry matter production and grain yield as compared with both the initial and standard densities. The role of foliage with respect to both maximum dry mater production and maximum grain yield was defined by an optimum range of relations between the rate of foliage development, leaf area, vertical structure and distribution of light intensity within the stand operating as a self-controlling system.

Potassium humate stimulated growth of wheat, increased the activity of phosphatase in the leaves and roots and and the activity of catalase in the roots.
A higher temperature (30° C) during cultivation caused a decline in the activity of phosphatase in the roots and leaves and a decline in the activity of catalase in the leaves. Anaesthetization of the embryos with chloroform retarded growth, increased the activity of the phosphatase only during the first days and increased the activity of the catalase. Similarly, removal of the endosperm caused growth to slow down. Wheat cultivated in this way had increased activity of catalase and phosphatase. The activity of phosphatase in the leaves of all variants and controls, was substantially lower than in the roots as compared with catalase, which was several times as active in the leaves as in the roots. Activity of catalase in both leaves and roots declined, in most cases, with age. Catalase activity declined with age only in the roots while it increased in the leaves.
The activity of the catalase is probably less dependent on the growth rate and depends rather on nutrition, the formation of chlorophyl, photosynthetic activity and like that. From both sources of reference and our experimental results, it can be seen that no simple relation exists between the activity of observed enzymes and the growth rate; the relationship is more complicated.

The paper deals with the study of morphological differentiation of flower buds in 10 varieties of apple-trees in relation to the growth of summer shoots and the earliness of varieties. The data obtained indicate that in the warmer regions of Slovakia the critical season of transformation of flower buds from vegetative to generative forms takes place, on the average, between July 20 and 29, and, at the same time, the variety Yellow Transparent deviates from the average four week-earlier. According to the author we can speak neither of a positive relation between the onset of morphological differentiation and the active growth of summer shoots nor of the relation between the earliness of the variety in maturing and the onset of differentiation. The morphological differentiation may be classified into five phases: 1^st phase - the formation of the growing point primordium, 2^nd phase - the formation of the cup on sepal primordia, 3^rd phase - the formation of petal primordium, 4^th phase - the formation of carpel and stamen primordia, 6^th phase - completion of the differentiation through substantial enlargement of flower organs before the onset of winter.

1. A number of varieties of cultivated juteGorchorus oHtorius L. andG. capsularis L. were tested in artificially created drought, waterlogging and control conditions.
2. The number of lateral roots with secondary growth was reduced to the minimum inC. capsularis under waterlogged conditions, but the weight of the roots was increased to the maximum, due to the production of numerous spongy and fibrous roots.C. olitorius suffered in both the characters under similar environment and failed to produce fibrous and spongy root. This species gained in root weight and lateral root number in drought under whichC. capsularis suffered in these two characters. These were the main features of adaptation of these two species.
3. Within species among varieties the variations regarding these two characters have been found to be controlled by genotypes. Lateral root number within both the species has been found to be a more strongly heritable character than root weight. Expected genetic advance has revealed the scope of selection for lateral root number.
4. While variations among thé varieties within species have been interpreted as an expression of phenotypic flexibility, the variation between species is an expression of phenotypic plasticity, which is an outcome of basically physiological mechanisms.Corchorus capsularis L. andC. olitorius L. are two cultivated jute species. The most striking distinction between these two species hitherto known is that whileG. capsularis can withstand waterlogging successfully,C. olitorius cannot. This general view formed the basis of testing these species under artificially created environmental stresses to find out the general components contributing to this specific difference.

Plants of two varieties of winter wheat-Besostoya 1 and Etoile de Choisie- were raised in the field. The same number of selected plants from each variety were frozen once in a refrigerator at a temperature of -15°C for 24 hrs. After freezing, the plants were gradually thawed and returned to the field. Early in the spring, test and control plants were treated with one of following diluted solutions: vitamin B₁, vitamin B₆, indolyl-3-acetic acid and adenine (the four solutions at a concentration of 0.01% and 5% urea solution in water) by immersion for 15 hrs. at a temperature of 18-20°C. The plants were measured in the spring and in the summer, the yield being determined after ripening.
It was found that all substances used helped to diminish the deleterious consequences of overwintering and to raise the yield of the plants. Vitamin B₆ exerted the strongest influence. Vitamin B₆ treated plants produced higher or slightly lower yields than those of the non-frozen control. Plants treated with vitamin B₁ gave yields close to, but in most cases lower than those of the non-frozen control.
The yields of plants treated with solutions of the remaining substances were appreciably lower than those of the non-frozen controls.
Plants of the more winter-hardy variety Besostoya 1 recovered relatively more easily under the effect of the substances used than the plants of the less winter-hardy variety Etoile de Choise.

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.

1. Protein synthesis in pollen tubes ofNicotiana alata Link etOtto estimated by the incorporation of leucine-¹⁴C is linear over six hours of artificial cultivation after a short lag phase. 2-Thiouracil and other growth-stimulating antimetabolites of natural pyrimidines and purines, such as 6-azauracil, 5-nitrouracil, 8-azaguanine and 8-azaadenine, stimulate the incorporation of leucine-¹⁴C into protein. The intensity of stimulation of protein synthesis is associated with the intensity of growth stimulation by antimetabolite.
2. Synthesis of RNA is inhibited by 2-thiouracil (according to the incorporation of uracil-¹⁴C, orotic acid-¹⁴C and³²PO₄ ^3- ).
3. Chloramphenicol (25 and 250 ppm) decreases during a one-hour treatment of pollen tubes the incorporation of leucine-¹⁴C by 12 and 24%, respectively. The same inhibition is found in pollen tubes stimulated with 2-thiouracil.
4. Pollen tubes incorporated 2-thiouracil into RNA. Stimulation of growth by 2-thiouracil can be reversed with uracil or uridylic acid.
These findings are related to the present views on protein synthesis and the mechanism of the chloramphenicol effect especially with respect to the possible explanation of the stimulation of protein synthesis during a simultaneous inhibition of RNA formation.
Physiological resistance of pollen tubes toward RNA antimetabolites, the relatively low sensitivity toward chloramphenicol, the contradictory change in RNA and protein synthesis due to 2-thiouracil and, further, resistance toward actinomycin D (Tupý, Süss 1965) point to the stability of the complex of messenger RNA with ribosomes in pollen tubes.

Mycelium of white-rot fungi secretes laccase into the medium. It was found by cultivation on malt-agar plates that the mycelium does not produce laccase equally in all its parts. The youngest hyphae at the margins of the colony represent usually the maximum producers, whereas older hyphae produce less or none at all. An exception here isCollybia velutipes which is the weakest producer of laccase of all the fungi studied and where only the older hyphae begin to secrete it. Manometric estimation of laccase showed that maximum specific activity of laccase is achieved at the boundary between the phases of initial and linear growth and i₁₁ some cases during the first half of linear growth. Ageing of the mycelium characterized by certain changes in its metabolism is reflected in changes of enzyme production by fungal hypha of different age.