Big vein disease occurring on lettuce plants cv. 'Pražan' was identified and the susceptibility to this disease was tested on 9 lettuce cultivars of foreign origin. Lettuce big vein virus was confirmed to be the cause of the disease. The transmission of the LBVV by the fungusOlpidium brassicae (Wor.)Dang., the sporangia of which were found by microscopy in the cells of surface tissues of lettuce roots, was experimentally proved. Rod-like particles, the average length of which was estimated at 244 nm, were found in the roots of diseased plants. LBW transmission by mechanical inoculation and by aphids could not be proved.

Funaria spores must structure their photosynthetic apparatus before germination. A lack of manganese in the culture media affects neither the final structure of chloroplast nor the chlorophyll synthesis. Fixation of CO₂, reducing power of chloroplasts (DPIP) and RPE photo-induced signal S II are modified by this lack of manganese. The study of Mn/Chl and CO₂ fixed/Mn ratios shows that Mn is a limiting factor for CO₂ fixation and that in the spores depleted of Mn the residual Mn is "structural" Mn.

In only one cultivar out of 1200 investigated cultivars ofPhaseolus vulgaris L. could we find an extreme change in the pattern of reserve proteins on the cathodic side: one of the proteins, called protein I, is completely absent in the cultivar 'Krupnaya sakharnaya' and is replaced on the same site by another protein,i.e. a protein completely different in its immunochemical specificity. The case is of interest from both the phylogenetic and systematic viewpoints and deserves further attention.

The main enzymatic oxidation products of IAA have been tested for biological activity, using as bioassay the straight-growth test ofAvena coleoptile. After being purified by rechromatography, none of these products (including methyleneoxindole) exhibited biological activity within the wide range of concentrations employed; consequently, the results accord with the evidence that IAA is the true hormone of plant growth.

Viable mutations affecting chlorophyll production in black gram (Phaseolus mungo L.) were recovered following treatments with X-rays and ethyl methanesulphonate singly or in combination. Of these theviridis mutant was characterized by viridine green colour of all the leaves and reduced plant size. inchlorotica the emerging leaves were initially yellowish green which gradually changed to dark green at flowering. The terminal 2-3 leaves always remained yellowish green inchlorina-terminalis whereas inchlorina-virescence the emerging leaves were yellowish green that changed to dark green at flowering. Inalbo-virescence the first 3-5 leaves at emergence were white in which small irregular green dots or patches often developed. The subsequent leaves were normal green. The emerging trifoliate leaves ofaureo-virescence were light green which turned to turtle green within a week. It was established thatviridis, chlorotica, chlorina-terminalis, chlorina-virescence, andalbo-virescence mutants were conditioned by a single receissive gene, in each case. Theaureo-virescence character was found to be inherited through the cytoplasm.

When examining plants of white mustard (Sinapis alba L.), a significant relationship between the size of the roots and the yield was found, both in a pot experiment and in a field one. The yield was influenced by the size of the root system during and after flowering time. Especially the number of seeds has increased, and the average weight of seeds showed the same tendencies after the flowering time. The productivity of plants with an above-average yield was increasing more quickly than the size of their root system. From the beginning of the vegetation till the end of flowering these most efficient plants showed the lowest permitivity dispersion and the highest dispersion after the flowering time. The dispersion has increased towards the end of vegetation.

Cytokinin-dependent and cytokinin-autonomous strains of tobacco callus tissue (Nicotiana tabacum L. cv. 'Wisconsin 38') were grown on media containing sucrose, glucose and fructose, respectively. The tissues were kept 14 days in darkness and then transferred for 9 days to continuous light after which time the fresh weight and chlorophyll content were estimated. The highest chlorophyll concentration was recorded at sugar levels which were either suboptimal (sucrose in the case of cytokinin-dependent strain) or supraoptimal (all other sugars for both strains and sucrose for the cytokinin-autonomous strain) for tissue growth. The chlorophyll concentration was increased when the tissue was cultured on media containing glucose or fructose,i.e. sugars whioh did not support the growth as well as sucrose. Chlorophyll synthesis in the cytokinin-autonomous strain is significantly lower than in the cytokinin-dependent strain. This difference was independent of either sugar source or concentration. These results support the observed inverse relationship between tissue growth and plastid development and the limited metabolic activity of plastids in cytokinin-autonomous tissues.

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 paper aims at verifying the possibility of obtaining seeds following placental pollination in more than 20 species of dicotyledons and monocotyledons. Excised placentae with ovules were cultivated in solid nutrient media in Petri dishes. Pollen was transferred from anthers onto placentae, its germinating capacity being enhanced by a drop of a 5 per cent sucrose in boric acid in certain cases. Fertilization of ovules resulting in the formation of viable seeds was obtained withNicotiana tabacum, Melandrium album andAgrostemma githago. Although withPaeonia officinalis, Viola tricolor, Antirrhinum majus, Galanthus nivalis, Narcissus pseudonarcissus, Clivia miniata andTulipa gesneriana normal seed set occurred, the seeds did not germinate even after being stimulated with GA₃. The results indicate that the findings may be used for further embryological studies. The species are listed in which no seeds were obtained.

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.

The effect of two different mechanisms of phosphorus ion transport from the nutrient solution volume to the surface areas of excised maize roots was studied under concentrations ranging from 0.01 mM to 50.0 mM KH₂PO₄. A modified technique of study of kinetic ion absorption was used. In the control series, the roots were placed in absorption solution without flow (the dominant mechanism of ion transport to the roots being diffusion), while in the experimental series the absorption solution was flowing round the roots at a rate of 0.162 cm s^-1 (the dominant mechanism of ion transport to the roots being mass flow). The rate of phosphorus absorption by the roots from flowing solutions was highly significantly increased at all concentrations of absorption solution except for the 50.0 mM KH₂PO₄ concentration. The increase in phosphorus absorption in the case of 50.0 mM KH₂PO₄ concentration was non-significant due to the fact that the high concentration of phosphorus together with the diffusion of phosphorus ions ensured a sufficient supply of phosphorus to the roots, covering the requirement for their uptake.
The results point to the need for an analysis of environmental factors to be carried out in studying ion absorption kinetics, and reveal the inadequacy of methods usually employed in such investigations, in particular with respect to the homogeneity of the nutrient solution in the whole of its volume and especially round the roots.

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.

The 2,4 dichlorophenoxyacetic acid (2,4-D) applied in solution (10μg per plant) on a leaf of lettuce plants (Lactuca sativa, cv. Grosse Blonde Paresseuse) decrease the translocation of⁴²K from the treated leaf, both in pretreatment and in simultaneous action if the interval of time is sufficiently long between the foliar applications. The metabolic action of 2,4-D seems to be located in the treated leaf. The results may be explained by a stimulation of the metabolic activity and consequently of the retention, already observed by several authors, with 2,4-D and other phytohormones. The 2,4-D had not a comparable effect on translocation of⁴²K from the leaves of maize plants (Zea mays Dekalb 202) even if the amount applied is higher and the duration of the pretreatment more important than previously. However, it must be noted for this species a light stimulation with 2,4-D on the retention of⁴²K in the sheath of the treated leaf. The results obtained with lettuce and maize might be fitted in a pattern of selectivity which appears for other aspects of the metabolism.

In controlled environment growth chambers, the effects of foliar and root applications of 2-chloroethyltrimethylammonium chloride (CCC) and 2,4-dichlorobenzyltributylphosphonium chloride (Phosfon) on the translocation of³²P fed to leaves, were investigated. When applied to leaves or to root, CCC had no effect on the relative amounts of³²P radioactivity retained by the fed leaf 5, 20 and 80 h after feeding. At 20 and 80 h after feeding, Phosfon concentrations of 0.01 and 0.1mg l^-1 reduced retention of the applied³²P. 80 h after³²P feeding, CCC concentration of 1 mg l^-1 applied as a foliar spray or to the root enhanced the downward movement of³²P. Phosfon at low concentrations, particularly at 0.1 mg l^-1, on the other hand, favoured an upward transport of the applied³²P. Foliar applications of CCC and Phosfon at high concentrations had no significant effect on³²P transport to the root and the shoot below the fed leaf, while root applications of CCC and of Phosfon inhibited downward transport. Root applications generally caused greater alterations in³²P distribution patterns than did foliar applications. On the basis of total active ingredient uptake, Phosfon was more effective than CCC in altering translocation patterns.