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.

Experiments with the growth regulator ethephon (2-chloroethylphosphonic acid) were made to stimulate the flower differentiation in the 'Carola' and 'Golden Delicious' apple cultivars in Pillnitz (GDR) and 'Jonathan' and 'Golden Delicious' in Ujfehértó (Hungaria). A twofold application of 150 ppm ethephon in June proved most effective. Our results indicate that it is possible to promote flower differentiation in apple trees without growth retardation and fruit thinning.

Wheat embryos floated off from organic solvents have been compared with mechanically isolated embryos. The results of comparative investigations, including germination,in vivo formation of polysomes and efficiency of cell free preparations forin vitro protein synthesis, favour the use of floated embryos for studies of biochemical processes during germination.

The application of 10^-3 g 1^-1 of 2,4 dichlorophenoxyacetic acid, 2-methyl-4-chlorophenoxyacetic acid, 3-amino-1,2,4-triazole and 6-chloro-2-ethylamino-4-isopropyl-amino-1,3,5-triazine toNicotiana tabacum cv. 'Samsun' plants inoculated with tobacco mosaic virus results in an increase in the content of this virus in the tissues. When whole plants are used, TMV content increases by 20% after herbicide application; when leaf dises are used, the amount of the virus can be doubled by the herbicide in comparison with control untreated inoculated discs. The results clearly show that the used non-selective herbicides act as stimulators of virus biosynthesis, probably via enhanced pentose phosphate cycle activity which enables an enhanced formation of viral RNA.

Free nucleotides of the primary root of maize were extracted with 5% HClO₄ and separated on a column of Dowex 1×8 ion exchanger in HCOO^- cycle. A two-step elution gradient (HCOOH, HCOOHNH₄) was used for the elution of the nucleotides. The incorporation of³²P into the nucleotides was followed at different time intervals and also in young and more mature root tissues. The nucleotides AMP, GMP, ADP, GDP, and ATP were identified. Labelled phosphorus was found in ATP after 30 s, in ADP after 3 min, and in AMP after 5 min incubation of the roots. More mature roots (18 days) contained higher amounts of AMP than the young ones (3 days).

The activity and localization of alcohol (AD), lactic (LD), malic (MD), isocitric (ICD) and succinic (SD) dehydrogenase, resp. was histochemically determined in shoot apices of plants in the vegetative condition during transition to flowering and at the reproductive state. The enzymes were determined in freehand sections, as well as in shoot apices incubatedin toto according toNachlaset al. (1958) using Nitro-BT. The characteristic localization of the enzymes depending on the ontogenic stage of the shoot apex is described. Different parts, layers and cell groups of the apex showed differences in enzyme activity. SD could not be detected in shoot apices. The histochemical findings are discussed in relation to former results obtained from a biochemical investigation of respiration in the same material.

If one cotyledon is removed from decapitated pea seedlings and the remaining one is treated with the cytokinin BA, then a complete correlation reversal occurs in numerous cases: instead of the bud belonging to the removed cotyledon, the bud belonging to the remaining cotyledon starts to grow. However, if GA is applied to the remaining cotyledon together with BA, then the number of these correlation reversals sharply drops. This in respect to cytokinin morphogenetically (correlatively) contradictory effect could play a significant role in apical dominance in plants.

The enzyme xylonase was used to isolate the protoplasts from the leaves ofCalendula officinalis L.,Gazania splendensMoore,Tithonia rotundifoliaBlake,Zinnia elegansJacq- and from the petals ofDahlia variabilis(Willd.) Desf. The recovery of spherical undamaged protoplasts differed. The same method did not lead to the isolation of the protoplasts from callus cultures derived fromCalendula, Gazania andTithonia leaves respectively.

The exposure of maize plants to drought led in most cases to a decrease in both the total and free water percentages, but to an increase in cell sap concentration, bound water percentage and bound water/free water ratio, comparing with the case of normal water supply. The employment of any of the studied treatments at either the normal or low soil moisture levels led throughout the period of time preceding the milky stage to a decrease in the free water percentage in maize leaves, but to the reverse effect with respect to both the bound water percentage and the bound water/free water ratio. The determinations of water fractions in leaves (free, bound water % and the ratio between them) before or at the tasseling stage appeared to be more reliable, compared with osmotic pressure determinations, as indication for the effective use of a given treatment in increasing the drought resistance of maize plants.

A technique is described for the establishment of infectious axenic callus cultures originated from stems of tobacco plants suffering from a mycoplasma disease, potato witches' broom. When stem pieces from a diseased tobacco plant (Nicotiana glaucaGrah.) are culture on a modified nutrient medium according toMurashige andSkoog (1962) with added kinetin (0.64 mg or 2.56 mg 1 000 ml^-1) and IAA (2 mg or 4 mg 1 000 ml^-1), the pathogen persists and spreads in the newly formed callus tissue. The presence of the pathogen was proved by implantation of callus slices into stems of tomato plants which indicate the disease very reliably. Reconstituted tobacco plants too recovered the infectious agent of potato witches' broom; 27 plants from the 35 reconstituted plants were diseased. Similar results were obtained with Crimean yellows. Calli were cultured and subcultured from 1 to 18 monthsin vitro and some infectious cultures are maintained and their investigation goes on. We suppose that kinetin plays a very important role for infectivity preservation in callus cultures.

The differences between leaves of different age according to their descending insertion level (starting from the youngest, 18th leaf) were compared with the changes occurring during the corresponding period of ontogenesis of the 18th unshaded leaf using the gas exchange [net photosynthetic CO₂ uptake (P _N ), water vapour efflux (E)] of the adaxial and abaxial surfaces of tobacco leaves as an example. Experimental elimination of the influence of shading during the involved period of ontogenesis of the 18th leaf manifested itself by a relatively slower decrease inP _N and by fluctuation of theE values at approximately the same level. Thus the differences between leaves of different insertion levels cannot be exclusively ascribed to the effect of their ontogenetic age.

Initially closed stomata in isolated leaf epidermal peelings ofCalotropis procera, Prosopis cineraria andTephrosia purpurea, opened when incubated in distilled water in light or in darkness. Water-induced open stomata closed down on incubation in abscisic acid (0.01 ppm) solution within half an hour. Sodium chloride induced the opening of stomatal aperture. NaCl-induced open stomata also completely closed down when incubated in abscisic acid solution, but open again when transferred to NaCl.

The effect of gametocides FW-450, maleic hydrazide and Dalapone on the course of microsporogenesis, gametogenesis and starch synthesis in pollen grains of winter rye ev. 'Esto' was investigated. Solutions containing various concentrations of tested substances were applied on leaves in amount of 2.5 ml and 5.0 ml per plant at the beginning, at the full and at the end of shooting. The effect of gametocides was detectable already in the phase of microspore formation when a decrease of anther weight, pollen grain size and starch content in grains and an increase of the number of microspores with nonfinished development were observed. The manner and the extent of injuries were dependent on the applied substance, its concentration and on period of its application.

Vicia faba plants cv. 'Erfordia' were treated with single application of CCC at 250 mg l^-1, 7 days before extraction. Such a concentration resulted in a 10.4, 14, 5 and 3.3 fold, respectively, increase in the levels of endogenous IAA, ABA, gibberellins and cytokinins relative to the controls. The results obtained indicate that a single application of CCC at a low concentration was sufficient to enhance the endogenous growth hormones in the treated plants. The results were obtained using GLC analyses for IAA, ABA and cytokinins, and the lettuce hypocotyl and soybean callus bioassay for gibberellins and cytokinins, respectively.

Humate (10 mg l^-1) supplemented to streptomycin solutions (0.1 and 1 mM) stimulates growth of germinating wheat and barley grains and of apical cuttings ofCrassula portulacea after 24 h treatment. It does not, however, prevent formation of albinic leaves. Albinism induced by the streptomycin alone and by streptomycin in presence of humate is irreversible and can be removed neither by an iron salt nor by a chelate added to the nutrition solution or applied on the leaves. Cells of plants treated with streptomycin and humate are larger than those of plants treated with the streptomycin alone. The same is true for plastids which in both cases are colourless and much smaller than chloroplasts of control plants. These plastids in a living or a fixed state have reduced ability to uptake stains. The albinic leaves are anatomically similar to chlorotic leaves of virus infected plants.

In Jerusalem artichoke tuber,in situ RNA synthesis along vegetative cycle shows two maximums. The first one appears during tuberization and installation of dormancy and a growth inhibition is sufficient to bring it about. The second reveals breaking of dormancy and precedes germination.

Callus tissue cultures were established from stems of tobacco plants (N. glaucaGrah.) both healthy and mycoplasma (potato witches' broom disease) infected on a modified nutrient medium (with a lower content of mineral salts) according toMurashige andSkoog (1962) in the presence of 2,4-D (1 mg l^-1) as a growth regulator. No differences were observed in the growth and development of both tissues. Organogenesis appeared on a nutrient medium (Petrůet al. 1972) supplemented with kinetin (0.64 mg or 2.56 mg l^-1) and IAA (2 or 4 mg l^-1). Callus derived from mycoplasma diseased plants started to form numerous buds after three months whereas organogenesis in callus from healthy controls appeared only after six months. We suppose that the reason of this difference is the fact that an expressively higher content of 2,4-D was found in the calli from healthy plants in comparison with the corresponding tissue from mycoplasma diseased ones. Reconstituted plants were isolated, rooted and transferred in the soil. The infectivity of these plants was assayed by grafting their stem tips on tomato plants which indicate very reliably and sensitively this mycoplasma disease. 31 reconstituted plants were obtained in the whole from calli isolated from mycoplasma infected plants and all of them were healthy.
It was established that mycoplasma failed in the presence of 2,4-Din vitro. Stem pieces from diseased plants in which mycoplasma presence was proved, lose their infectivity after 4 weeks of cultivation on nutrient medium with this growth regulator. On the contrary 2,4-D which spreads and acts especially through phloem (Smithet al. 1947) does not kill mycoplasmain vivo even in doses evoking strong symptoms of 2,4-D effect on experimental plants.

Cytogenetic effects of different concentrations of 2,4-D on suspension cultures ofVicia hajastanaGrossh. andHaplopappus gracilis(Nutt.) Gray were studied using a simple, chemically defined medium. InVicia, the frequency of dicentric chromosomes showed a negative association with the 2,4-D concentration. In both the species, the frequencies of anaphase bridges were negatively associated, while those of the diploid cells showed a positive association with the 2,4-D concentration in the culture medium. A decrease in the frequency of diploid cells was observed in the cultures transferred to a lower concentration of 2,4-D. This decrease was transient inVicia, while inH. gracilis a new equilibrium at a lower level was established. Both endoreduplication and selection appear to be involved in the achievement of the lower equilibrium inH. gracilis, although selection appears to be the major factor.

In squashes of broad bean and sunflower root tips, the staining with aluminium lake of nuclear fast red led to reliable results, comparable-otherwise-with the use of acetoorcein and similar procedures: the nucleus and ohromosomes are brightly red, the cytoplasm weakly pink.

The cytokinin-autonomous strain (A_s) of tobacco callus differs from the original cytokinin-dependent strain (D) and from the cytokinin- and auxin-autonomous strain (A₄) by a significantly lower activity of glucose-6-phosphate dehydrogenase (G-6-PDH). Changes in the total G-6-PDH activity were associated with differences in the number of G-6-PDH isozymes. The A_s strain contained only one isozyme, four isozymes were found in D and A₄ strains.