The RNA formed in pollen tubes during 4 hours of growthin vitro was resolved by chromatography on methylated albumine on kieselguhr (MAK) into three principal fractions. Acoording to the labelling from uracil-¹⁴C about 11% was eluted with tRNA and 5 S RNA (low molecular weight RNA), 76% just after rRNA (D-RNA) and nearly 14% was recovered from the column by SDS at 35 °C (TB-RNA). In the presence of actinomycin D at concentration of 30 μg ml^-1 the synthesis of the three classes of RNA was inhibited by 71%, 97% and 70% respectively. On sucrose density gradient the radioactive low molecular weight RNA sedimented at 4 S-5 S which suggests that one or both of these RNA species are synthesized in pollen tubes. The D-RNA eluted from the MAK column is polydisperse in size exhibiting a wide range of sedimentation values up to about 35 S with a large peak at 9 S-10 S and two smaller peaks at 14 S-15 S and at about 23 S. The rapid labelling and the polydisperse rather low molecular weight character suggest that the D-RNA is a heterogeneous population of mRNA. The sedimentation profile of TB-RNA was similar to that of D-RNA. The RNA synthesized in the presence of³²PBO3-₄ or uracil-¹⁴C exhibited no radioactivity peaks corresponding to sedimentation peaks of rRNA.

Behaviour of CMV, PVY and BYV was investigated in serological precipitin drop as well as gel diffusion reactions using crude extracts from infected plants and antisera against intact viruses. Gel diffusion reaction of PVY was positively influenced by degradation of viral particles with pyrrolidin while gel tests with CMV and BYV were influenced negatively. Antiserum and antigen titers of CMV, as determined in gel diffusion tests, were 4 to 8 times higher than in drop tests. The titer of PVY antigen, as determined in gel diffusion test, was the same as in drop test. Finally the titer of BYV antigen was 16 times lower in the Ouchterlony tests. On the basis of the ascertained differences in the behaviour of PVY and BYV the pyrrolidin degradation may be recommended for PVY but not for BYV. Diagnosis of PVY or BYV by testing crude extracts from infective sources for the presence of soluble antigen is not successful for the time being.

Peroxidase and polyphenol oxidase activities in malformed mango inflorescences of 'Himsagar' and 'Bombay green' oultivars wore found to be increased considerably following infection byFusarium moniliforme var.subglutinans. Whether such increased activities were due to their synthesis by the pathogen or the host, or both, was not studied although it was found that the pathogen was incapable of producing the enzymesin vitro. The activities of both the enzymes in infected tissues were found to increase considerably during the experimental period. It was found that activities of polyphenol oxidase were inhibited in the presence of sodium diethyldithiocarbamate and phenylthiourea; the former acted as chelating agent of Cu of the enzymes and the latter as a competitive inhibitor. Similarly, peroxidase activity was found to be inhibited by cycloheximide which acted as inhibitor of enzyme protein synthesis. The fact that the 'Himsagar' cultivar showed greater enzyme activity than the 'Bombay green' cultivar possibly suggests its higher resistance to the pathogen.

Treatment with cannabis induces a partial inactivation of the spindle apparatus, and an unequal separation of the chromosomes. There is more or less a tendency to с-mitosis at higher concentrations and to multipolar anaphases at lower concentrations like so many other narcotic substances. The MI value decreases linearly and sharply with the increase of concentrations used,i.e. cannabis had a severe mitodepressive effect. Long treatment for 24 h caused the death of all colls examined.
Cannabis causes a complete dissolution of the matrix substance of the chromosomes and breaks down the chromatin material of the nucleus to minute granules. This phenomenon was observed in all root tips treated with the cannabis. The same picture was observed after letting the roots recover in water.
The application of cannabis may disturb the extrachromosomal mechanism. This disturbance is restricted to the abnormal diffusion of the spindle organizers in many directions instead of two poles.

Suitable conditions for the fertilizationin vitro in maize have been studied. The germinating capacity of pollen in synthetic media was low; it was confirmed that it might be stimulated by supplementing agar with egg yolk. Application of pollen onto styles overhanging from the culture medium of excised ovaries was examined. After 5 days the styles could be cut off the ovaries, for the pollen tubes had already penetrated the embryo sacs. However, better results were obtained when cultivating ovaries along with segments of the maize cob. Solid media were more suitable for the development of kernels. Some of them germinatedin situ and gave rise to normal plants. From nucellar meristems of young kernels a callus could be derived which, on further cultivation, became green and regenerated shoots and roots. The cells of meristems exhibited a varying number of chromosomes.

The course of the transpiration flow rate (Q_w), of transpiration flow acceleration (Q_w/dt) and of the integrated transpiration flow was determined during an average summer day by repeated measurements according to the method of heat balance and the free water capacity of the tree trunk was estimated. The relations between the transpiration flow rate and the temperature and relative humidity of the air and the vapour pressure deficit measured at the same time in their diurnal course, as well as at the single diurnal terms during the whole time at which measurements were carried out were determined by correlation analysis. The problems linked with the effect of various meteorological conditions during different times of the day, of rain showers, solar radiation and soil water content are discussed. The possibilities of explaining the midday depression of transpiration on the basis of repeated measurements of the transpiration flow rate are evaluated.

The effect of 2,4 dinitrophenol and increased viscosity of the absorption solution on the absorption of phosphorus by excised roots of maize plants was investigated. The concentration of the solution was 0.1 mM KH₂PO₄, the activity of³²P was 52 µCi l^-1. The temperature of the absorption solution was 26 °C, pH 5.5, aeration prior to the experiment. There was 11 of solution for every 1 g of roots. Two basic variants were used for comparison: with non-flowing solution and with solution flow (circulation) of 0.162 cm s^-1, respectively. In all cases, 2,4 dinitrophenol reduced the rate of phosphorus absorption by the roots regardless of the mechanism of phosphorus supply to the roots (diffusion, mass flow). If it is proved that 2,4 dinitrophenol inhibits the active uptake of phosphorus, then the uptake of phosphorus by the roots increased under the influence of mass flow will be active,i.e., connected with energy metabolism.
Raising the viscosity of the absorption solution 3.3 times over that of water by means of potato starch substantially reduced the absorption of the phosphorus transported to the absorption zone by diffusion and practically did not affect the rate of absorption, or the amount of anions transported to the absorption area by mass flow.

Plants ofPlectranthus fructicosus were grown in two controlled environments -"spring" and "summer" conditions - differing in temperature and air humidity (day/night 20/15 and 27/22 °C; 80/98 and 50/80 % relative humidity) in order to study the influence of environmental conditions on the development of photosynthetic characteristics of individual leaves. The contribution of individual leaves to plant photosynthesis was very similar in both environments, the maximum shifting from bottom leaves to leaves of middle insertion levels during plant ontogenesis. On integrating the values of leaf photosynthesis for the whole vegetation period, the 5th leaf in "spring" conditions and the 4th leaf in "summer" conditions showed the highest contribution to plant photosynthesis (29 % resp. 25% of total net CO₂ influx). The "photosynthetically mature" leaves of middle insertion levels played the main role in CO₂ uptake of whole plant.

The role of exogenously supplied gibberellin (GA₃) and cytokinin (benzyladenin -BA) in the correlation between the mature leaf and its axillary bud was investigated in one-node segments ofHydrangea. When both leaves were left on the segments, then both GA and BA were able to determine the dominance between axillary buds, that means that the bud treated with the corresponding growth regulator grew more vigorously. When one of the leaves was removed, the bud belonging to the removed leaf grew more vigorously, but GA applied onto the axillary bud belonging to the remaining leaf caused a complete correlation reversal: the bud belonging to the remaining leaf grew more vigorously. On the contrary, the application of BA onto the bud of the remaining leaf resulted in only insignificantly stimulated growth of the bud belonging to this leaf.

Considerable changes in tryptophan synthase aotivity occur during the ontogenesis of pea plants (Pisum sativum L.) in their individual parts. Maximal tryptophan synthase activity is connected with the vigorous growth period of the individual organs and of the entire plant. The content of free serine which is present in excess and is one of the substrates in the reaction catalyzed by tryptophan synthase, also changes, as well as the content of free tryptophan, the product of the reaction. The changes in the contents of these amino acids do not correspond to the variation in tryptophan synthase activity and mainly follow the alterations in the total nitrogen metabolísm. The limiting factor in the biosynthesis ofL-tryptophanin vivo is probably the availability of the aromatic precursor, above all of indole-3-glycerophosphate. The content of bound tryptophan also shifts in the pea plants owing to the enrichment of proteins in older parts of pea plants with this amino acid.

Uptake of magnesium was studied by continuous flow technique for 82 days old rice plants in nutrient solution over a range of 0.2 to 1 ppm or 8.2 to 41 µM magnesium concentration. Uptake of magnesium followed a Michaelis-Menten kinetics with a Michaelis constant, K_m of 0.2 × 10^-4M and V_m 156 µg g^-1 h^-1. With increasing flow rate, the rate of magnesium absorption was increased.

The treatment of rice seeds with 0.02% proline increased the germination under saline conditions.

Activities of RNasea were studied in cotyledons of dormant and afterripenedAgrostemma githago seeds. Activity of RNase increases during imbibition and germination. This increase in activity cannot be observed in variants which are not able to germinate (dormant seeds and seeds blocked by higher temperature). The development of RNase activities during germination cannot be inhibited by concentrations of cycloheximide or actinomycine D completely preventing phosphatase synthesis. These results may be indicative for the assumption that the increase of RNase during germination is caused by enzyme activation and not by enzyme synthesis. Cytokinins and a combination of cycloheximide and gibberellic acid stimulate the activity of RNase in dormant cotyledons, whereas neither cycloheximide nor gibberellic acid, applicated by themselves, show any effect. Cytokinins and gibberellic acid do not influence the activity of RNase of afterripened cotyledons, abscisic acid inhibits the increase of enzyme activity.
There are characteristic changes in the pattern of RNases during germination revealed by polyacrylamide gel electrophoresis. The increase in RNase activity of dormant cotyledons caused by cytokinins is accompanied by obvious changes in the RNase pattern on polyacrylamide gel. Treating dormant cotyledons with cytokinins dormancy is partially overcome. In consequence of the application of cytokinins the differences in the electrophoretic RNase pattern between dormant and afterripened cotyledons can be nearly balanced.

High accumulation of³²P was observed in the leaves of intact gherkin plants 9 days after their roots had been treated with 0.005% suspension of the systemic fungicide Folcidin 50WP (cypendazole),i.e. 8 days after the roots had been exposed to labelled phosphate. Folcidin also influenced phosphorus metabolism in the plants. High biologic cytokinin-like activity of the fungicide was established when using a callus cytokinin bioassay.

Thes-triazine herbicides studied (atrazine and simazine) inhibited the growth of the seedlings ofTrigonella foenum graecum L.(Viciaceae). These herbicides caused a decrease in the contents of total water soluble carbohydrates and reducing sugars. Pentose sugars increased in the cotyledons. The total protein and free amino acid contents were enhanced. The activity of peroxidase was inhibited in the cotyledons, but was enhanced in the seedling axes.

Water stress in the leaves was induced by gradual decreasing of substrate moisture in five-day cycles.The hydration level of the leaves was characterized by their water potential (ψ_w), osmotic potential (ψ_s), pressure potential ψ_p and water saturation deficit(ΔW _sat ).The activities of Photosystems 1 and 2 were determined polarographically with Pt/Ag(AgOH) electrode as changes in oxygen concentration in chloroplast suspensions. The shape of light curves of Hill reaction was not influenced by leaf (ψ_w), hence both quantum efficiency and dark phase of this process were affected in a similar manner by water deficit. The activities of both photosystems measured at saturating photon flux density declined with the lowering of leaf (ψ_w) (in the range from -5 to -14 x 10⁵ Pa) and the decrease in activity of Photosystem 2 was more rapid than that of Photosystem 1. The ratio of activities of Photosystems 1 and 2 was mildly enhanced by a lowering of (ψ_w), but it decreased with increasing age. The lowering of ψ_winduced lowering in the chlorophyll a/b ratio thus concealing the usual ontogenetic course of this ratio.

In cotyledons ofChenopodium rubrum L. polydisperse RNA is synthesized in the region of the low molecular weight RNAs during photoperiodic induction. After short-time labelling the rate of 4s RNA synthesis was always higher in induced plants than in plants having obtained a light-break in the middle of the dark period. When glucose was added to the nutrient medium during the dark period of a single photoperiodic cycle the rate of nucleic acid (NA) synthesis was higher in non-induced plants than in induced ones at the termination of the dark period. In plants induced by two cycles in the absence of glucose the rate of NA synthesis at the termination of the second dark period was higher in induced than in non-induced plants. This difference is due to the differential kinetics of NA synthesis during darkness. In plants induced in the presence of glucose the peak of the rhythm in NA synthesis was advanced by 4 h relative to that found in plants induced in the absence of sugar. Thus, the termination of the dark period coincided with the negative slope of the oscillation in plants induced in the presence of glucose, while in plants having obtained a light-break NA synthesis decreased only slightly after having attained its peak. In plants induced in the absence of glucose the termination of the dark period coincided with the peak in the rhythm in NA synthesis. The rhythm in NA synthesis of the cotyledons during the dark period of an inductive cycle is out of phase with the rhythm in flower initiation.

The level of RNA in pollen is approximately 20 mg g^-1 and remains constant during 6 h pollen germinationin vitro also in the presence of 2-thiouracil which stimulates pollen tube elongation. The synthesis of RNA in pollen tubes was investigated according to the incorporation of the label from uracil-2-¹⁴C, 2-thiouracil-2-¹⁴C, orotic acid-5-³H, fructose-U-¹⁴C and from³²PO₄^3- into RNA fractions separated by methylated albumine kieselguhr chromatography. The distribution of radioactivity on elution profiles was different according to the radioactivity source, however it was not changed by the presence of 2-thiouracil in cultivation medium. 2-Thiouracil incorporates into pollen tube RNA at about 50% the rate of uracil. It inhibited the incorporation of orotic acid, of fructose and of phosphate into all RNA fractions. It is suggested that the analogue inhibits the enzymes involved in RNA synthesis essentially as 2-thiouridine-5'-phosphate.