The employment of the classic stand density experiments in studies of the horizontal organization of plant stands is very laborious and requires a large experimental field area. The procedure based on the regular thickening of plant stands is more convenient for plants grown in a lower density. A simplified modification of this method is described which keeps a constant square nutritional area regardless of the plant densities.

Both CCC and cold (5°C) treatment gave rise to an increased content of the water-soluble proteins in leaf tissue of the winter rape, irrespective of the day length. This effect was accompanied by a decrease of the insoluble nitrogen compounds content, mainly under theLD (the 16 hour day). The applied retardant also stimulated the consumption of the structural compounds induced by low temperature.
Low temperature treatment hardened plants more distinctly than the CCC application. The frost hardening effect of CCC andSD (the 8 hour day) was manifested only at 20°C and it disappeared at 5°C.
Changes in frost hardiness were not correlated with the changes in the reducing sugar content and in the reducing ability of the studied tissue. The coincident effect of CCC and cold on the reducing sugar content was observed underSD conditions.

Barley seeds were treated with ethyl methanesulphonate (EMS), washed for 24 h, redried to 15 per cent moisture and stored at 25°C. The criteria used for expressing the effect of storage were chromosomal aberrations in root tips, M₁ germination, M₁ seedling height, M₁ survival and the frequency of M₂ chlorophyll mutants. The increase of the M₁ biological injury due to storage was not influenced:
a) by applying EMS solutions at pH 2, pH 7 and pH 10,
b) by lowering the EMS concentration and increasing the treatment time,
c) by different variations of washing with water and by washings with 0.005 N NaOH, 200 mM cysteine or 200 mM thiourea. The rate of the increase of the M₁ injury due to storage depends on the EMS dose. With a decrease in the EMS dose the storage effect is more delayed.

The influence of photoperiodic induction on the incorporation of uridine-³H into the shoot apices ofChenopodium rubrum was studied using the technique of autoradiography. No increase in uridine incorporation was detected either during induction lasting three days or immediately after its termination. Pyroninophylia likewise did not rise. However, changes in uridine incorporation related to morphogenetic activity during leaf formation and later during differentiation of inflorescences were well marked. The distribution of label in the nucleus immediately after three inductive cycles shows the ratio of extranucleolar to nucleolar incorporation to be higher in non-induced control plants than in induced ones.
Data from literature pointing to an activation of RNA synthesis during transition to flowering are discussed and compared with other systems where ontogenetic changes are accompanied by marked changes in RNA synthesis. It is assumed that the activation of RNA synthesis after induction is connected mainly with the activation of growth. However, inChenopodium rubrum photoperiodic induction proceeds together with limited growth and without activation of RNA synthesis.

Nitrate reductase (NO₃R) activity, nitrite reductase (NO₂R) activity and NADH₂ dependent glutamate dehydrogenase (GDH) activity were followed in extracts from excised pea roots incubated under aseptic conditions for 9 and 24 h in nitrate containing nutrient medium to which IAA was added in concentrations promoting lateral root formation (1 × 10^-5; 3 × 10^-5; 5 × 10^-5 M) and kinetin in concentrations which reduce lateral root formation (0.1; 1; 5 mg 1^-1, that is 4.65 × 10^-7;4.65 × 10^-6 and 2.3 × 10^-5 M). NO₃R activity was not influenced by IAA, NO₂R activity was slightly depressed by IAA after 24 h incubation and GDH activity was slightly increased after 24 h incubation in the presence of IAA. Kinetin decreased NO₃R activity significantly both after 9 h and 24 h incubation, slightly increased NO₂R activity after 9 h incubation but slightly decreased it after 24 h incubation, and did not affect GDH activity after 24 h incubation. However, when applied together with IAA, kinetin abolished the promoting effect of IAA on GDH activity. IAA neither reversed nor accentuated the effect of kinetin on NO₂R activity. Nevertheless the depressing effect of kinetin on NO₃R activity was emphasized by the presence of IAA after 9 h incubation. The results obtained indicate that reduced nitrate assimilation due to the depression of nitrate reductase activity caused by kinetin probably contributes to the negative growth effect of kinetin in pea root segments grown in nitrate medium.

The root surface determined microscopically amounts only to ten per cent of the surface assayed with methylene blue. This difference is assumed to correspond to the sorption surface of cell wall interfibrillar capillaries. The volume of these capillaries amounts to 0.1 per cent of the total volume of the organ only, but their surface far exceeds the external root surface. It is suggested that the interfibrillar capillaries of the epidermis cell walls constitute the main elements of the root sorption surface.

No influence of IAA on the endogenous estrogen content in bean plants was stated. At the same time kinetin was found to increase and abscisic acid to decrease the amounts of estrogens.

To study the effect of high altitude cosmic radiation the seed material of 15 species ofAcanthaceae was subjected to 3 types of exposures in balloon flights at an altitude of 30 900 to 38 100 metres. Germination behaviour was recorded and cytological studies were made. In the material subjected to one exposure, no detectable cytological or morphological change could be recorded. Material subjected to two exposures showed a 1 1/2 to 2 fold increase in cellular dimensions. A fragmented chromosome was observed inRostellularia procumbens. Flowering inJusticia betonica was advanced by 3 weeks. Among the species subjected to 3 exposures, two species showed diminution in height, and entered into flowering earlier than the controls. A study of germination behaviour showed, in general, that the decrease in germination percentage was directly proportional to the amount of radiation. The results indicate that the treatment with cosmic radiation may be helpful in reducing the period between sowing and harvesting. Therefore, if similar experiments be conducted on crop plants, they might yiled interesting and important results from the agricultural point of view.

The transpiration rate of detached leaves exposed in the atmosphere saturated with water vapour increased after a certain time. This time as well as the shape of the transpiration curves varied according to the duration of the exposure of the leaves in the humid atmosphere.

Highly active NAD-MDH (E.C.1.1.1.37) and low activity of NADP-MDH (E.C.1.1.1.40) were found inVicia faba roots. The NAD-MDH activity is associated with 6 to 12 isoenzymes. The number of isoenzymes is dependent on the extraction (use of Triton X-100etc.) and detection procudures (presence of KCN, phenazine methosulphate). The meristematic zone does not contain one isoenzyme (X) which is present in the other two zones. The meristematic zone, elongation zone and zone with the beginning differentiation differ in their activity of individual isoenzymes.

The constant values of water potential gradient accompanying various levels of water flow rate were found in kale leaf tissue segments. This constancy might indicate the decrease of resistance to water flow as flow rate increased and this decrease of resistance was confirmed.

The stem pith discs of kale and tobacco were cultured on simple sugar-mineral media. The dry weight of the expiants rose almost linearly for 20 days and was doubled in 10 to 12 days. Neither protein accumulation nor the increase in cell number are responsible for this relatively high increase in dry weight of discs. The accumulation of sugars or polysaccharides is thought to be the cause of this increase.

The effect of CCC and GA₃ on the growth and development of spring wheat (Triticum aestivum L.) cultivated under predominantly red (500-700 nm) or blue (400-500 nm) light was investigated. Red light enhanced the development of wheat during the exponential phase of growth. This effect presumably implicated the promotion of gibberellin synthesis under red light. The strong inhibitory action of CCC under red light (the inhibition was lower under blue light) might be interpreted in a similar way. The growth became more intensive under blue light after caring and was accompanied by increased susceptibility to giberellic acid treatment.

The presence of native cytokinins was studied in growing apices of apple-tree annual shoots. During June the presence of two compounds showing cytokinin activity in biotest was observed and their R_F value was determined in three chromatographic systems.

Germination ofPinus banksiana seeds is controlled by the photoreversible phytochrome reaction. The seeds, even unimbibed, are sensitive to red light. At 660 nm, the energy required to promote germination to the same order of magnitude is much higher for unimbibed seeds than for the imbibed ones. In both cases it is possible to reverse the effect of a single red light irradiation by applying far red light (730 nm).

The interaction of GA and IAA in apical dominance was investigated in an experiment in which first of all an IAA paste was applied to the cut areas formed by the decapitation of epicotyl apices of pea seedlings, followed after one week by the application of a 0.25 % GA paste. The latter treatment was able to overcome the growth inhibition of cotylary buds induced by a 0.03 % IAA paste, but not that caused by 0.06 and 0.12 % IAA pastes.
The correlative function of a root in the renewal of the apical dominance can, to some extent, be directly simulated by exogenous gibberellin, as has been demonstrated in the experiment with decapitated pea seedlings deprived of one cotyledon, on which the growing axillary of the amputated cotyledon was decapitated. In this case the axillary of the remaining cotyledon grows in the plants where the root has been left, but in those deprived of the root, there appears a serial of the amputated cotyledon (Dostál, Biol. Plant. 9 : 330, 1967). When GA was supplied to the plants treated in this way, the coty lary of the remaining cotyledon grew even in the plants deprived of the root.

The variability of the incubation period of the beet mosaic virus [Beta virus 2(Lind) Smith] was investigated in a three year experiment. The virus was transmitted by the black bean aphid (Aphis fabaeScop.) or by a mechanical inoculation onAmaranthus caudatus L. Variability characterized by the standard deviation indicates a closer distribution of measurements when the virus was transmitted by mechanical inoculation. The differences in variability of the incubation period between the two methods of virus tramission are statistically significant; dispersion and standard deviation are lower after mechanical inoculation. The average length of the incubation period after virus transmission by aphids and by mechanical inoculation was 10.8 and 7.7 days, respectively. The difference was found statistically significant and may be explained by the higher number of viral particles transmitted by mechanical inoculation which may accelerate the process of infection. A significant correlation between the temperature of the environment and the length of the incubation period was also found in some experiments.

The effect of nutrient solutions with certain essential elements lacking, on oxidation reduction potential (RP) of the first leaf was examined in two cultivars of barley seedlings NO₃^- and K⁺ decreasedRP considerably, PO₄^3- did not. The effect of NO₃^- and K⁺ was dependent. on the illuminance. Under glasshouse conditions, the increased level of NO₃^- and K⁺ did not cause any change ofRP. In field conditions, the increased supply of nitrogen fertilizers resulted in a lowerRP in leaves at ear emergence and a higher yield. The use ofRP measurement in leaves for the estimation of the effect of mineral nutrition on plants is discussed.

Using regression analysis a proof of the relation between the electric capacitance and the root surface in maize, sunflower, oats and onion plants was given. This dependence is possible to exploit in the selection of plants (of the same population grown under the same conditions) for a well-developed root system.

Changes in the percentage of seed germination, the growth and respiration rate of the seedlings were observed at 15-day intervals from the stage of the full germination capacity of rice (Oryza saliva L.) seeds till they became non-viable. At the beginning, the respiration rate changed but little, but afterwards, with the approach of non-viability, the rate declined sharply. A positive correlation of respiration with a decrease in the germination percentage and the length of seedlings and a negative correlation with days of storage were also established. A strong correlation existed between catalase and peroxidase activity with respiration, indicating that the activity of these enzymes can be used as an indicator of metabolism, and therefore can be considered as part of the respiratory mechanism of rice seedlings.

The present report is focused on the study of participation of exogenous DNA in the process of postirradiation reparation of meristematic cells ofVicia faba primary roots. It is aimed at comparison of the positive reparative effect of isologous DNA with postirradiation action of heterologous DNA in its native, thermally denatured and DNAase-degraded forms, or DNA degraded by ultrasound, and with the effect of other biologically important macromolecules (RNA, histone, heparin, and dextran sulphate). For this purpose, the roots ofVicia faba irradiated by 150 r exposure were cultivated in solutions containing the above substances for an appropriate time interval. In squash slides both mitotic activity of the investigated cell population and frequency of postmetaphase chromosomal aberrations induced by radiation were evaluated. It was shown that a stimulation of cell division and reparation of chromosome damages were supported exclusively by isologous DNA. On the contrary, exogenously applied heterologous DNA increased postirradiation frequency of aberrations; maintenance of native structure of applied DNA was an essential condition for the above effect. Other macromolecules investigated on the course of postirradiation reparation ofVicia faba meristematic cells were without effect.

Physiological effects of volatile substances released by the overground as well as by the underground organs of higher plants were studied. The activity of the volatile substances was tested both when these substances were allowed to act directly in the air and when they were dissolved in water in the form of solutions. Plants which do not contain essential oils or which are not rich in them as well as those abounding in essential oils and other volatiles were used in the experiments. The physiological activity of the volatile substances was tested on rye seedlings.
The overground as well as underground mature organs of the tested plants were found to release volatile substances causing, when acting directly, in the majority of cases an inhibition of the growth in length and of the formation of dry matter in rye seedlings. A pronounced inhibition of the growth of rye seedlings was brought about especially by the volatile substances of "aromatic" plants such as common dill, wild thyme, yarrow milfoil, garden thyme, marjoram, etc. The volatile substances released by the organs of "non-aromatic" plants like sugar-beet, common sunflower, quackgrass, etc., were found to bring about a significant inhibition of the growth of rye seedlings, too.
The volatile substances released by the plant organs were found to be altogether absorbable in water and physiologically active also in the form of water solutions. With the exception of volatile substances from hemp and quackgrass leaves, which brought about a mild stimulation of the dry matter formation in rye seedlings, inhibitory effects of these solutions were found to prevail in all cases. Most effective were the solutions of the volatiles from some of the "aromatic plants".
An assay for olefines in the atmosphere of the experimental vessels demonstrated that in almost all cases ethylene is being released by the plant organs.

Changes in the variability of quantitative characters (number of fertile stems, length of the stem and of the spike, number of spikelets in the spike, number of seeds in the spike and in the spikelet) in M₂ induced with 0.1 mM, 0.2 mM and 0.3 mM N-nitroso-N-methylurea (MNH) and with 5000r and 10 000 r of X-rays inTriticum monococcum L. var.sofianumKörn. were evaluated. The mean of the populations remained practically unchanged by the mutagens whereas the variability increased considerably with increasing concentration or dose. Changes in the variability were more pronounced in the values for the first stem than in the values for the first three stems. When changes in the population mean were found (with some of the most elevated concentrations and doses), these changes were shown to be mostly due to a repetition of the cultivation, whereas the changes in the variability were mostly due to the action of the mutagens. In all experimental populations, mutations in quantitative characters were successfully induced.

Some biochemical properties ofTrigonella foenum-groecum infected withPeronospora trifoliorum have been investigated. Qualitative changes were observed in lipids, coumarins, amino acids and indole compounds only. A quantitative study of the phosphate content was also carried out. Neutral lipids did not show any significant changes. In addition to the fourteen phospholipid bands, the infected leaves contained a new band corresponding in R_f to phosphatidic acid or polyglycerophosphate. Seven coumarins were present in both the extracts. In addition 3-hydroxy coumarin, 5-hydroxy-4-methylcoumarin and 7-hydroxy-4-methyl-coumarin were detected in infected leaves. Higher levels of indole acetic acid and three of its derivatives were observed due to infection. Infection altered the free amino acid content. Tryptophan appeared and the total phosphate content increased. Increase in phenols and indoles suggest a higher respiratory rate whereas a higher content of inorganic phosphate suggests uncoupling of phosphorylation from respiration.

The shoot apex or fruitlets of Jonathan apple trees grafted on M IX rootstock and grown in pots in a greenhouse were exposed to¹⁴CO₂ in an assimilation chamber. The translocation of¹⁴C-labelled assimilates from treated organs to other parts of the plant was studied.
It was found that a very small amount of¹⁴C-labelled compounds was translocated from the shoot apex and very young fruitlets to the shoot stem. Preliminary chromatographic studies show that the chemical composition of the labelled substances detected below assimilation chamber differs profoundly from that of those remaining in the supplied leaves. The results support the view that there exists a translocation of some substances, possibly regulators from the sink to the donor.

Antonovka seedlings were obtained from the embryos soaked in abscisic acid (ABA) alone, gibberellin A₄₊₇, benzyladenine or the mixtures of these regulators. The inhibitory effect of ABA on the growth of the seedlings was of temporary duration. The height of the 12 week-old seedlings was dependent only on the degree of seed after-ripening and not on the ABA treatment.
The growth stimulators studied were unable to overcome the inhibitory effect of ABA observed in the early stages of seedling growth. The growth stimulators did not substitute, for cold treatment of apple seeds which is the only treatment so far known to overcome the dwarf conditions of the seedlings obtained from non-after-ripened embryos. ABA greatly suppressed the early stages of apple seedling growth (up to 6 weeks) during which they resembled physiological dwarfs.
The highest concentrations of ABA (2.0 μg ml^-1) greatly modified the root system of the seedlings, and produced a larger percentage of seedlings with unbranched roots.