The investigation of phosphorus absorption by intact plants during a short period has above all confirmed the validity of the results obtained in the foregoing study of the kinetics of absorption by excised roots. Further, the results show the unquestionably important role of mass flow in transporting ions to plant roots, mainly at lower and medium concentrations, that is, from about 0.1 to 10 mM. Under conditions of growth close to the optimum, the supply by means of mass flow can be sufficient even at lower concentrations of phosphorus, such as 1.47 mM KH₂PO₄, or the absorption of phosphorus by plants can be higher than in the case of ions being transported to roots by diffusion. With a higher absorption the phosphorus distribution somewhat changes as well, relatively more of it being accumulated in the roots. 2.4-DNP applied to the nutrient solution at a concentration of 10^-5 M reduces the phosphorus absorption.

Spraying the growth retardant (B-9) ranging from 500 to 4000 ppm, on caraway and fennel plants reduced stem height, whereas increased the umbel number per plant. There was a slight increase in seed-yield as well as weight of 1000 seeds of the two umbelliferae plants, induced by B-9. The largest values of volatile oil, crude fat, and carbohydrate in the seeds of the two plants resulted from 4000 ppm B-9. Whereas, the crude protein was not affected by B-9 treatments in both plants.

The cytological effect of one of the alkaloid of Opium, namely morphine sulphate onAllium cepa root tips from a qualitative and quantitative point of view were studied. It was found that morphine sulphate caused partial effect on spindle formation and also showed a mito-depressive effects particularly after long treatment.

The transpiration rate of intact spring barley plants, cv. Profesor Schiemann resistant to powdery mildew was studied separately in light and in darkness. At the first stage of pathogenesis the fungus temporarily reduced the transpiration rate of the host plants in light (E₁). The transpiration rate in darkness (E_d) was not influenced in this period and only in the period of formation of necrotic spotsE_d in the host plants was somewhat higher than that in the control plants.E₁ of the host plants gradually reached the level of the control plants in this period. The fungus considerably reduced the rationE₁/E_d. The differences in this ratio between infected and control plants increased in the susceptible cultivar but were moderated in the course of necrobiosis.

Six to seven-day-oldNostoc sp. strain 221, I.A.R.I. cultures leach out considerable quantity of urea in the culture medium while only detectable quantity of urea was noticed in algae cells.

Changes in the transpiration rate of intact spring barley plants, cv. "Slovensky dunajsky trh", were studied separately in the light and in the dark under controlled temperature and illumination, after the infection withErysiphe graminis DC, during an 8 day period of the development of the fungus. In the first stage of pathogenesis, the fungus diminishes water output from the host plants in the light. An opposite phenomenon can be observed in the dark; water output from infected plants in the dark increases sharply mainly in the stage of advanced fructification. Thus, the fungus considerably diminishes the ratio of water output from the host plants in the light to that in the dark.

The experiments showed that after gamma irradiation as well as after irradiation by secondary cosmic rays (hard component)Equisetum arvense spores produce in the first developmental phases prothalia at a changed rate,i.e. in favour of the females. This effect being specific for radiation cannot be produced by heat, pressure or changes of electric and magnetic field (i.e. factors appearing in higher sea levels with a stronger intensity of cosmic rays). It will be possible to apply the sensitivity of the mentioned method for investigating the problems of testing cosmic ray variations. The possibility of its application in spontaneous variability research is not less important.

Salicylic,p-coumaric, and ferulic acids were detected in the acetone-insoluble cell fraction, presumably protein, extracted from the brown discoloured tissues of rice (Oryza sativa L.) leaves infected withPyricularia oryzaeCav. but not from healthy leaves. It is proposed that these phenolic acids are oxidizedin vivo in blast diseased rice leaves, and forms a protein-quinone complex.

During the histochemical investigation of dehydrogenases in the developing shoot apex of wheat plants it was found that the morphologically similar cells of the peripheral meristem may be differentiated according to the differential activity of alcohol dehydrogenase. While the enzyme was not present or exhibited a very small activity only in the tissue of leaf primordia it was highly active in the cells of bud primordia irrespective of the degree of their development and their differential physiological determination.

Hydroxylamine added to the nutrient medium in sublethal concentrations (0.2 to 1.0 mN) enhanced NADH₂ dependent glutamate dehydrogenase activity in isolated pea roots. The increase in activity depended on proteosynthesis and was lower in the presence of NO₃^- and NH₄⁺ ions. The induction of nitrate reductase and of nitrite reductase was partly inhibited by sublethal hydroxylamine concentrations.

Chimeral plants with variegated leaf blades were obtained by induction of organogenesis in primocultures of leaf explants ofNicotiana tabacum L. cv. Burley 49, chlorophyll mutation White Seedling. Only green plants regenerated from primocultures of explants taken from dark green leaf areas of the chimeras. The possibility of a multicellular initiation of chimera regeneration from tissue cultures is discussed.

The content of carbohydrates and activities of phosphatases onN. tabacum cv. 'Samsun' inoculated with Y-virus were studied. Dynamic manner of the systematic studies allowed to find new immediate connections. The results of this experiments with the results of our previous investigations gived the explanations of the varying content of carbohydrates in the tissues. The investigated time period of 10 day were divided into 2 parts with breaking point arround fourth day. During the first part at the decreased activity of hexokinases and at the increased activity of phosphatases the accumulation of saccharides in tissues was observed. During the second part slightly increased activity of phosphatases could not supply to the very stimulated kinases the sufficient amount of carbohydrates so that the content of saccharides considerably was being reduced untill the rate of the control plants.

The influence of Cu²⁺ ions (in the form of CuCl₂) in the concentration range 10^-3 to 10^-6 M on the content and biosynthesis of indole glucosinolates glucobrassicin and neoglucobrassicin has been studied on etiolated seedlings of rape (Brassica napus var.arvensis(Lam.) Thell.). Ions Cu²⁺ acted on the seedlings either chronically from the beginning of the germination or acutely, during 3 to 72 h, on seven days old seedlings. The biosynthesis of both glucosinolates was followed by the incorporation of³⁵S from Na₂³⁵SO₄ into them in hypocotyl segments from seven days old intact etiolated seedlings. After the entry of small amounts of Cu²⁺ ions into the plants, stimulation of the glucosinolates formation occurs, as was found after three h action of Cu²⁺ ions. After the entry of a greater amount of Cu²⁺ ions into the plant, harmful effects appear, as was found after chronic two days action or after 24 and 48 hours acute action of Cu²⁺ ions. Later further stimulation of glucosinolate formation occurs, probably due to enhanced metabolism during reparation processes, as was manifested after chronic action of Cu²⁺ ions lasting four and eight days. The optimal effect of copper was found mainly in the concentration range 5×10^-4 M to 10^-5 M.
Ions Cu²⁺ in higher concentration increased the uptake of sulphate ions by hypocotyl segments, and in lower concentrations increased the incorporation of³⁵S from³⁵SO₄^2- into the proteins.

The roots ofAllium cepa L. were treated with water solutions of cyanein and griseofulvin for 24 and 48 h respectively, thereafter cultured for 48 h in the medium without the antibiotics, and the reversibility of the inhibition caused by the antibiotics was evaluated. Changes in the mitotic index of meristematic cells were followed in squash preparations of root apices. In addition to the cytologic observations, the differentiation of the primary meristem was followed in longitudinal sections. After the treatment with reversible doses of cyanein and griseofulvin respectively, differences were found in both the effects of the antibiotics during the treatment and the restoration of the inhibited processes after the treatment. In the cells treated with cyanein the restoration of mitotic activity was instantaneous but less intensive and in|complete especially in the case of the 48 h treatment. After the treatment with griseofulvin which temporarily interfered also with the differentiation of the primary meristem, the restoration of the inhibited processes was delayed but intensive after both application times, 48 h after the treatment no symptoms of the preceding inhibition could be observed.

Using the quantitative serological method of double diffusion in agar, the amount of sugar beet yellows virus in the leaves of sugar beet was investigated and the possibility of an accurate serological analysis was examined at certain time periods in the course of vegetation. In sugar beets infected artificially at the beginning of the vegetation period the increase of the titre has a fluctuating course at first. In August, after the intensive growth of plants is over, the virus content maintains on a relatively high degree, increasing further toward the end of vegetation. For a reliable virus analysis the sap can be diluted approximately in the ratio 1/128. The table presented enables one to determine the probable accuracy of the serological analysis at the individual time periods during the vegetation of sugar beet.

The supernatants obtained after the centrifugation of the homogenates of healthy barley leaves and the extracts from the surface of barley roots can enzymatically oxidize exogenously supplied IAA in the presence of Mn²⁺ ions and 2,4-dichlorophenol. On the contrary, IAA oxidation is strongly inhibited or does not occur at all in the supernatants from the leaves infected with powdery mildew (Erysiphe graminis DC.) and in the extracts from the surface of both healthy and diseased leaves. The supernatants from diseased leaves inhibit IAA oxidation proportionally to the amount of the added supernatant. That indicates that natural inhibitors formed in the course of infection are present. In the case of the roots, the enzyme obviously penetrates to the surface of the organ. The presence of the enzyme on the surface of the leaves could not be proved either for its low concentration or owing to the presence of the above-mentioned inhibitors.

Phototropic sensitivity of forest wood seedlings to lateral illumination was proposed as an early assay for distinquishing various ecotypes of woody plants of the same species. Statistical analysis showed that results were significantly influenced by heterogenity of experimental material caused by an interference of phototropic movements and natural oscillations of hypocotyl. Both movements of pine seedlings (Pinus silvestris L.) were registered by phase photography and their mechanism was analyzed. The apical part of growing hypocotyl illuminated from above oscillates in a space spiral with frequency 3.3 h at mean growth rate 0.66 mm h^-1. The mean size of spiral amplitudes is 2.9 mm. The oscillation rhythm is disturbed after the lateral illumination and a phase shift was observed as a result. A new oscillation rhythm with frequency 3.9 h and mean growth rate 0.69 mm h^-1 was stabilized after a period of time equal to one nutation turn. Oscillation amplitudes were increased to 4.3 mm.
In addition to the radiation intensity the appearance of the phototropic response to light pulse is first of all effected by the actual position of the apical part of hypocotyl in the course of endogenous circumnutations. A uniform plant material for the early assay may be obtained by selection of seedlings which are at the beginning of lateral illumination in the same phase of nutation rhythm. Under such conditions the deviations of longitudinal axis of oscillating spirals characterize the actual phototropic curvature.

The endogenous auxin-like substances were analyzed in the shoot extracts of young spinach seedlings, exposed to photoperiodic induction. At least eight indole auxins were found. One of them was identified as tryptophan, the other one is most probably IAA. The plants grown in long days had a higher level of ether soluble auxins than the controls in short days. Separate extractions of plants after each of the eight inductive days showed that the auxin content was not constant, but subjected to irregular oscillations. However, parallel oscillations were also found in control plants grown in short days. Staminate plants were found to contain more endogenous auxins than the pistillate ones. It is concluded that the quantitative changes in auxins during the photoperiodic induction are probably not related to flowering, but to some other growth process, common to all plants in that phase of growth. The higher level of auxins in staminate plants may be the cause of their faster elongation before the onset of flowering.

The growth of coleoptile sections ofTriticum and its stimulation by indole-3-acetic acid (IAA) are inhibited by 5-azacytidine added into the cultivation medium. 50 per cent depression of the elongation was observed at 2×10^-3M 5-azacytidine concentration. Thymidine kinase activity in cell-free extracts prepared from coleoptile sections treated with 5-azacytidine, and caleulated per 10 mg of their wet weight, is increased while IAA administration resulted in its depression. The observed changes in thymidine kinase activity can be explained assuming the different uptake of water due to 5-azacytidine and IAA treatment.

3 peaks of DNA synthesis were observed in the barley embryo of seeds, germinating for 49 h in running tap water at 25°C. The first peak, found after 22h, was formed by S-cells in the roots and in the 1st leaf meristem. The second peak (after 34-37h) and third peak (after 46-49 h) represents the S-cells in the roots, apex and 1st, 2nd and 3rd leaf meristems. Application of N-methyl-N-nitrosourea for 3 h at the onset of germination inhibited the rate of DNA synthesis and postponed the peaks of DNA synthesis in individual meristems of the embryo.

The cytochalasines B and D inhibit the hyphae elongation ofSaprolegnia monoïca but the ramification power is not affected. A false hyperramification becomes very clear. The cytochalasines B and D do not stop the translocations of stimulators or inhibitors in the young mycelium. The cytochalasine D has a greater eficiency than the cytochalasine B.

Kinetin (KIN) and benzyladenine (BA) stimulate to different extent the germination of apple embryos isolated from dormant seeds or seeds submitted to stratification. KIN is much more active in the replacement of light requirement in apple embryos germination. Both cytokinins decrease the photosensitivity of embryos isolated from the seeds stratified less than one month, but only BA accelerates the appearance of the second photosensitivity maximum, normally occuring on the 70th day of stratification. Both cytokinins stimulate the activity of acid phosphatase between the 30th and 50th day of apple seed stratification. The stimulation between the 50th day and the end of stratification is exerted only by KIN.
These differences allow to discuss the specificity of action of particular cytokinins during the after-ripening and germination of apple embryos.

Starch degradation inNicotiana tabacum cv. Samsun infected with PVY was studied with respect to the formation of Glc-6-P which serves as a starting substrate for glycolysis and pentosephosphate cycle. Enhanced activity of these two metabolic pathways at the time of maximal reproduction of the virus requires an increased content of this substrate which is probably produced mainly by the hexokinases. The results of this paper indicate that Gle-1-P, synthesized during starch degradation, is not the main intermediate enabling an enhanced activity of the pentosephosphate cycle, because despite a high starch content in the tissues only a decreased amylophosphorylase activity was found. However, an appreciable amount of Glc-6-P at the time of maximal reproduction of the virus results from enhanced phosphoglucomutase activity.
As there is not enough Gle-1-P for an enhanced activity of this enzyme due to the lowered activity of amylophosphorylase and because its curve resembles activity curves of the hexokinases (published in the previous paper), this result could be explained by the presence of galactose and by the presence of an enzyme system which would be able to metabolize it to Gle-1-P.Additional index words: Nicotiana tabacum, respiration, glycolysis, pentosephosphate cycle.

Three strains of three different species of chlorococcal algae(Chlorella kesslerii Scenedesmus quadricauda andScenedesmus obliquus) were compared in their physiological and genetical responses to N-ethyl-N-nitrosourea (NEU). The mutagen was applied in the basic doses corresponding to their specific tolerance to it. Exponentially-graded doses derived from the basic ones acted for the same period of time and single basic doses acted at linearly-increased periods of time in parallel experiments. The influence of the mutagen on the cell cycle just in progress was characterized by the increase in the frequency of cell divisions which yielded a lower number of autospores. The conditions of the cells during the first three days after treatment were determined according to the average increase of their lag phase. The relative toxicity of the mutagen was expressed as the survival frequencies. The mutation effects were evaluated according to the frequency of permanent changes observed in the growing cell colonies : lethal, morphological and pigmentation. NEU was found to be a relatively suitable mutagen for the chlorococcal algae studied.