Treating scooped out bulbs of hyacinths (Hyacinthus orientalis L. cv. 'Lady Derby', cv. 'Pink Pearl', cv. 'Delft Blue') and tulips (Tulipa gesneriana hort. cv. 'Oxford') with cycloheximide stimulated strongly the infection of the tissues of the bulbs byPenicillium sp. The possible mechanism of such an activity of cycloheximide is discussed.

MLO containing invaginations were found in protoplasts of phloem parenchyma cells in symptomless young leaves ofRibes houghtonianumJancz. infected with a yellows disease. The invaginations originate between the cell wall and plasmalemma, usually at plasmodesmata, and change apparently into superficial vesicles in the protoplast; they are entirely or partially limited by host plasmalemma. The formations mentioned occur in parenchyma cells which contain normal organelles. Sometimes they are divided by a smooth membrane system enclosing MLO. Besides MLO the invaginations contain in some cases slimy fibrils resembling the P-protein in sieve tubes. The MLO bodies seen in invaginations have usually a diameter of 50-250 nm and their plasmalemma (unit membrane) is identical with the plasmalemma of MLO bodies occurring in sieve tubes. However, only few MLO bodies in invaginations are electron dense, so that they resemble naturally degenerated forms of MLO. Similar MLO containing invaginations were formerly described from some leafhoppers transmitting MLO.

The relationships between DNA synthesis and germination capacity ofAgrostemma seeds have been studied. Protein synthesis and RNA synthesis are activated at the very beginning of imbibition, whereas DNA synthesis starts in the second part of the imbibition phase.
Agrostemma seeds inhibited by higher temperature (30° C), or aged seeds with a low germination capacity are characterized by a remarkably reduced protein synthesis. DNA synthesis is also reduced. The inhibition of protein-synthesis ofAgrostemma embryos fed with cycloheximid or actinomycin D causes a depression of DNA synthesis. These results indicate that the initiation of DNA synthesis of imbibingAgrostemma seeds depends on the synthesis of special proteins. Abscisic acid inhibits growth as well as DNA synthesis of isolatedAgrostemma embryos. Mitomycin inhibits germination and DNA synthesis to the same extent. Dormant seeds with an undiminished intensity of protein synthesis also show a reduced incorporation of³H-thymidine in DNA. We suggest that DNA synthesis of imbibed seeds, which is a necessary prerequisite for the radicle protrusion, is involved in the mechanism of afterripening of theAgrostemma seeds.

The increase in the measured transpiration rate in tobacco leaves due to the experimentally decreased humidity of the bulk air was found to be significantly lower than the theoretical value calculated from the change of water vapour concentration gradients. Boundary layer and stomatal diffusive resistances remained unchanged under experimental conditions with no change of net photosynthetic CO₂ uptake. This suggests an increase in intercellular diffusive resistance with an increase in water vapour concentration gradient which is the driving force of water vapour diffusive part of transpiration flux.
The increase can be ascribed to the lengthening of intercellular diffusive pathway as steeper water vapour concentration gradient in intercellular spaces results in an increased evaporating surface of intercellular cells thus moving the effective plane of vaporization in leaf mesophyll further inwards. Due to different and independent changes of concentration gradients for water vapour and CO₂, different length of intercellular diffusive pathways for CO₂ and water vapour may be expected.

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.

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.

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.

Tartaric acid is synthesized on light in the leaves ofTamarindus indica L. and is translocated to the flowers during flowering seasons. The translocation of this acid to fruits keeps peace with their growth rate. The decline of the tartaric acid content per unit fresh weight in mature fruits is not due to their utilization or conversion, but largely due to the setting up of the seeds which are devoid of any tartaric acid. Tartaric acid content in both the leaves and fruits show variation in different seasons, while malic acid does not show any change excepting a small increase in March.

Leaf angles, frequency distribution of leaf area inclinations, leaf area index, amount of intercepted radiation, biological, vegetative and grain yields and grain yield proportion of biological yield were determined in maize stands of two population densities, 55 555 plants ha^-1 (S₁), and 80 000 plants ha^-1 (S₂). Also the effect of the artificial change of leaf angle upon these indices was studied. We classified normal maize stand (N) as the interstage between a planophile and a plagiophile type of canopy, that with artificially changed leaf angle (V) as an erectophile type of canopy. The relative interception of the incoming radiation in the variantsV S₁ andV S₂ was lower than in the variantsN S₁ andN S₂. The variantsV in comparison with variants N increased grain yield and biological yield.

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.

The manner of regeneration phenomena of carpophores ofCoprinus congregatus planted on the fresh nutritional substrate was studied. In the cultures taken from the carpophores that had completed their development the first viable regenerated primordiums appear mainly on the mycelium developed from the carpophore-implant (indirect regeneration). On the contrary, in the cultures taken from the carpophores in which the final morphogenesis was checked by unfavourable conditions, temperature or light, the first regenerated structure developed essentially on carpophore-implants (direct regeneration). It appears that a relation exists between the regeneration potential an development of the phenomena of maturation in carpophore-implants.

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.

Respiration of protoplasts isolated from the leaf mesophyll ofPetunia hybrida was estimated by the Warburg method. The time course of respiration rate shows an initial decrease followed by a prominent increase which is caused by shaking of the protoplast suspension. The absolute respiration rates are low and show an unusual spread, but the temporal form of the curve is always similar to that one shown in Fig. 1.
The RQ-values shift from below 1 during the initial phase to far above 1 during the increase of the respiration. For isolated protoplasts from petals the same is true. Feeding the protoplasts with DNA does not influence the respiration rate significantly. The physiological quality of protoplasts seems to suffer in a high degree from the isolation process.

A non-specific effect of antiviral factor (AVF) was proved by interference of five different viruses (CMV, PVX, PVY, TMVe, TMV vulgare) with CBRV.
The non-specific AVF originates in non-infected tissues around TMV lesions. Transmitted mechanically to other plants this AVF exhibits the same suppressive effect on multiplication of TMV and CBRV.
The AVF is formed in the non-infected apical part of the leaf which was infected in its basal region. The susceptibility of leaves is decreased even when AVF is added to virus inoculum and applied mechanically on the leaf. The apical part of the leaf the base of which is met with necrotic reaction to TMV, is considerably less susceptible and TMV multiplication in this region is decreased. The necrosis on the leaf base induced by mechanical injury or by cysteine hydrochloride may decrease the susceptibility of the leaf to some extent, but has no effect on multiplication of the virus.
The activity of AVF in healthy apical region of the leaf increases till the fifth to the eighth day after its basal part was infected. The apical region then exhibits lower susceptibility (decrease in number of lesions) and the growth of lesions is decreased. This indicates the virus multiplication being suppressed.

In comparison with controls, the respiratory activity in locally infected leaves was lower until the 8th day after inoculation, whereas it was higher with the leaves in which systemic infection was expected. In the course of the remaining period of investigation, the respiratory activity was almost identical in both cases, showing a rising tendency. Ascorbic acid oxidase whose activity curves correspond to those of respiration, represents the main terminal oxidase. Its activity is probably coupled to the respiratory chain in which glutathione, reduced by NADPH, is capable of reducing reversely dehydroascorbic acid originating from the action of ascorbic acid oxidase. Virus Y-infected plants containing excess NADPH, as found out in our previous paper, the respiratory chain mentioned is likely to be utilized preferentially.

Humic acids can inhibit the activity of wheat phytase in model experiments, because they are able to form complexes with hexainositol phosphates and have considerable adsorption properties. Decarboxylated humic acids do not show any inhibitory effects.