In contrast to their soil counterparts, algal fulvic acids were more inhibitory than the corresponding humic acids. Fulvic and humic acids fromFucus vesiculosus were more efficient than the correspondingLaminaria digitata acids in inactivating the enzyme.Laminaria humic acids, which have no phenolic hydroxyls, showed a concentration dependent inhibition hardly in accordance with the presumed role played by these groups in the activity of oxidases.

Time-lapse microcinecmatography showed that the negative prototactic response of the chloroplast lasted 11-19 min and was completed 40 min after the beginning of irradiation; the contraction reached 11% in 60 min.

A propagation method for someFreesia cultivars usingin vitro cultures is described. Bud and root formation was evoked in callus tissue culture on a modified Murashige and Skoog's medium. Reconstituted plants were transferred into soil and cultivated in the glasshouse.

The tips of the rhizomorphs ofSphaerostilbe repens transferred on agar medium regenerate some aggregated organs without an intermediate mycelium stage. Each extremity of the drawn rhizomorphs can give rise to eoremia on its air face and to rhizomorphs on the contact with tho culture medium. These heterogeneous environmental factors impose polarized regeneration, easily inverted, upon the rhizomorphs. Nevertheless, a residual and stable polarity remains; it is attributed to the apex which is more capable of bearing new organs than the other extremity. Tho efficiency to regenerate depends on the ago of collulos and on tho size of tho rhizomorph tip; howover it is very difficult to provent the formation of new aggregated organs.

Uridine-³H incorporation and RNA concentration were investigated in different parts of the shoot apical meristem ofChenopodium rubrum using autoradiography and cytophotometry. A single inductive cycle was sufficient to bring about postinductive first events in the shoot apex but not for complete flower differentiation. The initial activation of RNA synthesis manifested itself in all zones of the apex. The first increase was more conspicuous in the peripheral than in the central zone. The indications of the first events in the apices after a single inductive cycle disappear prior to morphological reversal to the vegetative state. Induction by three short days led to rapid flower differentiation. The increase in RNA synthesis and concentration was most conspicuous in the central zone in this case. The ratio of RNA synthesis and content between bud and leaf primordia (B/L) also change in relation to photoperiodic induction. In vegetative plants the B/L ratio was low while after induction it increased.
The shifts in activity of RNA synthesis observed in the shoot apical meristem are related to the changes in growth activity of the different parts of the apex. The growth ratios in the apices bear the character of growth correlations. The change in the growth correlations following photoperiodic induction together with the total activation of RNA synthesis are considered to represent one of the first events of the transition to the reproductive state.

The effect of mannitol, glucose and sucrose on the stomatal behaviour of two desert species,Merremia aegyptia andM. dissecta has been studied. Stomatal opening did not uniformly depend on the decrease in turgor of the epidermal and subsidiary cells caused by the different osmotic potential of the sugars. Sucrose caused plasmolysis of the subsidiary cells only but this was not accompanied by the opening of the stomatal pore. InM. aegyptia, no plasmolysis was seen either in epidermal or subsidiary cells, even the stomata opened; inM. dissecta, on the other hand, plasmolysis occurred in these cells without any stomatal opening, after incubation in glucose or mannitol. Mannitol is least absorbed, glucose slightly more and sucrose is absorbed to a very large extent in the guard cells when the materials were inoubated in the respective sugar solutions. However, the absorption of these three sugars was almost always larger in isolated epidermal strips than in discs; in detached intact leaves it was still more reduced.

The effect of gibberellic acid, benzyladenine and a mixture of these compounds on the activity of some hydrolytic enzymes was studied in hyacinth bulbs non-exposed to low temperatures. Plant growth regulators were applied on the heel of dormant bulbs in the middle of July. An intensive elongation of the inflorescence was observed only in the plants treated previously with GA₃ and grown in a warm greenhouse for 63 and 84 days. The activities of amylase, invertase and acid phosphatase were higher in the flower buds of unrooted bulbs treated with growth regulators than in the control plants, although growth regulators did not affect the level of extractable proteins. The elongation of the inflorescence in the plants treated with gibberellic acid was correlated with a sharp increase of invertase activity in this organ. The effect of GA₃ and BA on the activity of other enzymes in buds and scales varied with the period of plant growth.

Total activities of nitrate and nitrite reductases were higher in 4 to 20 day old maize plants in the leaves than in the roots. The ratio of activities found in the leaves and in the roots respectively was much higher in the case of nitrate reductase than in the case of nitrite reductase. On the other hand higher glutamate dehydrogenase activity in the roots than in the leaves clearly indicates that the roots play a more important role in the assimilation of ammonium than in the assimilation of nitrate. When comparing the distribution of seminal and nodal adventitious roots of maize seedlings with the assimilation of inorganic nitrogen on the basis of enzyme levels, it could be deduced that during the first 20 days of seedling growth seminal roots were more involved in the assimilation of nitrate whereas nodal adventitious roots were more active in ammonium assimilation.

Soybean (Glycine max (L.) MERR. CV. 'Amsoy') plants were grown for 40 days in nutrient solution at various concentrations of ammonium. Maximum yield of dry matter was obtained at a concentration of 715 μM. Further increase in the concentration of ammonium resulted in a reduction in growth due to ammonium toxicity which affected both root and shoot development. The pattern of nitrogen accumulation in tops was consistent with the multiphasic uptake of ammonium and can be represented by 2 phases in the range 1.78 X 10-⁵-3.57 x X 10-³ M of ammonium.

Chemotropic effects exerted by metal cations have been investigated simultaneously with their influence on the increments ofSinapis alba roots cultivated in dark and light. The effects of Na-EDTA and Na-humate and its fractions, as well as the interaction of these substances with cations have also been studied. Chemotropics have been administered in agar-agar to the ends of roots growing on glass plates. Chemotropic and growth effects were exerted by Cu²⁺, Fe²⁺, Fe³⁺ and Ca²⁺ cations. The light strongly changed the effects of all but Cu²⁺ cations. Both Na-EDTA and humante appeared to be active chemotropically and generally abolished the effects of cations, although in some cases Na-EDTA made this influence more intense. Of the humate fractions, only those characterized by the ability to form complex compounds appeared to be active. No correlation has been found between chemotropic effects and the influence on the growth of roots, except for the Cu²⁺ cations, which always caused positive chemotropism and inhibited the growth of roots.

Application of 1 ppm zeatin raises the respiration rate (measured by the Warburg method) of leaf mesophyll protoplasts ofPetunia hybrida by about 50% after 4 h; afterwards there is a rapid decrease. While the rate of respiration in the controls rises after 5 to 6 h, 1 ppm zeatin has a strong inhibitory effect. When the protoplasts are incubated with 0.1 ppm zeatin the rise in the rate is much slower, and after 7 h the rate is 30% higher than in the controls. Abscisic acid (10 ppm) decreases the respiration rate so that after 5 h it is less than half that of the controls. Later on there is a rise as in the controls, perhaps caused by senescence promoting effects of abscisic acid. The photosynthetic rate of the mesophyll protoplasts measured by¹⁴CO₂ fixation decreases with increasing age of the preparation. The protoplasts previously incubated with zeatin for 1 to 3 h show an increase in photosynthesis: with 0.1 ppm zeatin the¹⁴C-fixation rate is higher the longer the hormone could operate. With 1 ppm zeatin we get a typical optimum curve similar to that for respiration. These optimum curves indicate the inhibitory effect of high concentrations of zeatin on respiration and photosynthesis.

Treatment of two-week-oldBrassica campestris andTrigonella foenum-graecum plants with morphactin andVicia faba, Antirrhinum orontium, andPapaver somniferum with Niagara, induced marked variations in the orientation and ontogeny of stomata and the epiderma cells. Morphactin-chlorflurenol at 12.5, 62.5, 125, 250, and 500 ppm, caused marked damage of the shoot apices and changes in the epidermal tissue, such as divisions of the guard cells, reduction in the size of the stomata, and epidermal cells. Niagara-ethyl-hydrogen-1-propylphosphonate at 100, 500, 1 000 5 000, and 10 000 ppm caused thickenings of the epidermal cell walls and differentiation of new meristemoids from the epidermal cells, contiguous stomata, and incomplete development of the guard cells.

The results presented in this paper indicate an immediate relation between the increased activity of the pentosephosphate cycle and the biosynthesis of the virus. In the period of its maximal reproduction (4 to 8 days after inoculation) also pentosephosphate cycle activity is enhanced what enables an increased biosynthesis of both purine and pyrimidine nucleotides which are necessary for the formation of the viral RNA. As soon as the period of the maximal reproduction of the virus ends, the activity of the pentosephosphate cycle drops deeply under the value of the control. The lowered intensity of respiration at the period of intense reproduction of the virus could be then explained by a decrease in the content of ADP-either on the level of its biosynthesis or by its preferential incorporation into the RNA of the virus-necessary for oxidative phosphorylation connected immediately with respiration. The courses of glucokinase, fructokinase and sucrase activities also correspond to the activity of the pentosephosphate cycle; these enzymes supply a sufficient amount of substrate for Glc-6-P dehydrogenase. The increased glycolysis activity from the 12th day on probably balances the energetic deficit in host metabolism caused by virus reproduction.

In a study on the phenolic distribution of rice husk (lemma, palea, rachilla and sterile lemmas), seven phenolic acids were detected in the alkali and alcoholie extracts. The total quantity of phenolic compounds in the husk differed with cultivars; however, no qualitative difference was noticed.

In 7 species (Eleocharis palustrisR. Br.,Juncus bufonius L.,Gypsophila muralis L.,Trifolium repens L.,Agrostis stolonifera L.,Potentilla anserina L. andAchillea millefolium L.) growing in a gradient of habitats from aquatic to terrestrial, on a sandy fishpond shore in Southern Bohemia, Czechoslovakia, the daily course of transpiration rate and water content was assessed gravimetrically in their cut-off transpiring parts on two typical summer days. Transpiration rate was largely controlled by microclimate but depressions occurred inJuncus and in some species growing in the drier habitats. The highest instantaneous transpiration rate and total daily transpiration per unit dry weight, about 100 mg g^-1 min^-1 and 50 g g^-1 d^-1, respectively, were recorded inAchillea andTrifolium. The water turnover rate ranged from 16.1 g g^-1 (H₂O) d^-1 inJuncus to 10.7 inGypsophila. The estimated daily maximum water saturation deficit was highest inEleocharis (45.7%) and lowest inAchillea (15.0%). The adaptational significance of the observed phenomena is discussed.

The changes of content and some chromatographic characteristics and biological activities of natural free cytokinins were studied during the vegetation season in the growing apices of apple tree shoots. Biological cytokinin activity was discovered in two groups of compounds differing in the time of their biological actions. Rf values and in the time of their maximal content in the growing apices. The time of maximal content was in accordance with their biological activity.

The occurrence of beet mild yellowing virus (BMYV) on feeding- and sugar-beet in Czechoslovakia has been proved. The virus was transmitted by aphidMyzus persicae (Sulz.) on indicator plantsSinapis alba L.,Capsella bursa-pastorisMedik, andClaytonia perfoliataDonn and from these plants back to sugar-beet cv. 'Dobrovická A.' A weed plantRaphanus raphanistrum L. was identified as a new natural host plant of BMYV. The virus was identified in ten of twelve biologically examined samples of beet with BMYV-like symptoms, which were collected at various places in Czechoslovakia

A modified procedure for the extraction of betacyanin fromAmaranthus seedlings is described. Application of this modification increased the absorbance of cytokinin-treatedAmaranthus explants in most cases. The modifiedAmaranthus test is compared with the soybean callus test in the bioassay of kinetin, 6-benzylaminopurine, and 6(δ,δ-dimethylallyl) aminopurine.

An installation is described enabling measurements of photosynthesis, transpiration and dark respiration, and estimation of photorespiration rates at different carbon dioxide and oxygen concentrations, at different irradiances and leaf temperatures.

Effects of various concentrations of streptomycin sulphate either alone or in combination with different cations and hormones on mungbean (Phaseolus aureus L.) seedling growth were studied. The relative inhibition of root growth was stronger than that of hypocotyl growth. Root growth inhibition was completely overcome by calcium, while other cations were ineffective. Inhibition of hypocotyl elongation could not be prevented by cations. IAA and GA₃ were capable of relieving streptomycin inhibition but kinetin was ineffective.
In the coleoptiles of streptomycin-treated rice (Oryza sativa L.) seedlings, there were accumulation of nucleic acids and decline in protein content resulting in increased RNA/protein and DNA/protein ratios. High nucleic acid content induced by streptomycin could be correlated with reduced activity of the nucleases.

The content of substances showing the cytokinin activity was estimated on decapitated and one-cotyledon-deprived pea plants during that period when the promoting effect of the cotyledon excision had not yet been manifested. Results of the bioassay showed that after the excision an increase in the level of substances with cytokinin activity occurred only in cotylars growing in axillas of these excised cotyledons. These results coincide with earlier data about the content of gibberellins and auxins in the same object.