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 characteristic micromorphology of the tobaoco cell strains, or its cyclic changes in the course of the subcultivation interval can be affected by auxin composition of the medium,i.e. by the application of either 2,4-D alone, or NAA, or their combination. On omitting one of the auxins, the over-all growth of the cultures is not substantially affeoted; however, the participation of various oell types, as well as the occurrenoe of starch grains are altered. The presenoe of 2,4-D alone results in an inhibition of starch occurrence, NAA alone causes a stimulation. There is no causal dependence of the occurrence or absence of starch grains on the stimulation of elongation (volume) growth, or, on the contrary, on cell division.

The treatment of the bark of regularly tapped trees with 2-ohloroethylphosphonio acid (CEPA) in the long run brings down sucrose level in the latex even when latex production is not increased. The sucrose deficit thus caused persists for a number of months after the treatment probably due to the depletion of carbohydrate reserves by the stimulation. The loss of carbohydrates not related to an increase of rubber produotion grows as the concentrations of applied CEPA are raised.
The treatment increases the activity of phosphoenolpyruvate (PEP) carboxylase and decreases pyruvate deoarboxylation in mitochondria-free oytoplasmic latex serum. The pyruvate deoarboxylase has a sharp optimum at pH 6.5 and is almost inactive at pH 7.5 while PEP oarboxylase, like invertase, has the optimum at weakly alcaline pH and is only slightly active at pH 6.5. The CEPA-induced changes in the activity of these enzymes are related to an increase of latex pH after the treatment. Consistently with this the evolution of CO2 from sugars catabolised in the serum was found to decrease with increasing pH.
It is concluded that the observed ethylene-induced changes in enzyme aotivities bring about in latex vessels a deviation of the glycolysis-fed metabolio flux from synthetic pathways to mitochondrial oxidations and consequently a decrease in the efficiency of sucrose conversion to rubber.

The effects of acetylcholine (Ach) on growth, the total peroxidase activity and the isoperoxidase spectrum of the roots ofLens culinaris were studied and compared with actual and earlier results obtained with an auxin (IAA) treatment. The general growth and peroxidase activity patterns of Ach treated roots and IAA treated ones showed many important similarities.

Tubular structures showing honeycomb-like appearance in cross sections were found in mycoplasma invaded sievetube cells of abnormal sprouts of apple trees infected with the proliferation disease. The nature of tubular structures is unknown. There is a striking similarity (or identity) with the tubular structures described formerly in HEp-2 cells which were established from human carcinoma of the larynx.

Additional three plant species were found to be natural hosts of a necrotic TMV. strain,Silene inflata SM.,Melandrium albumGarcke andAtriplex nitensSchkuhr.

Light induces the formation of pycnidia inPhomopsis mali. The induction caused by light can be conserved in darkness. The size and quantity of pycnidia vary with the illuminance. Under low and high illuminances physiologically different pycnidia appear.Phomopsis mali cultivated in darkness in the presence of other microorganisms (fungi or bacteria) can fructify and produces pycnidia similar to those formed under low illuminance and in natural conditions. Our experiments indicate the presence of a pycnogenesis-inducing substance that can exists in different forms and induces the formation of the different pycnidia.

The water potential (Ψ _w ) and the water saturation deficit (δW_sat) in leaves of different insertion levels of potted kale plants were simultaneously measured. In non-wilting plantsδW_sat gradually decreased andΨ _w slightly increased from the upper to the lower leaves. During the wilting of the plants induced by decreasing of soil moistureΨw practically decreased paralelly in all the leaves but the same decrease ofΨ _w was connected with the lowest increase ofδW_sat in upper leaves and the highest increase ofδW_sat in lower leaves. Not only the values ofΨ _w andδW_sat but also their relationship varied considerably with the leaf insertion levels.

Taking into consideration simultaneous infection of tomato leaves withCladosporium fulvumCooke and TMV, the fungus infection inhibits the TMV reproduction. This inhibition occurs in the plant irrespective of the sequence of pathogen inoculation and reaches even 70 per cent. The fungus spores applied to the TMV purificate inhibit the TMV infection, as well.

Healthy and mosaic infected leaves ofL. nudicaulis have been cultivated onMS and modifiedMS media (MC). Profuse growth and differentiation of tissue have been obtained onMS medium in diseased tissues as compared to the modified medium. It has been found on bioassay that although there is no difference between the concentration of the virus in tissue culture and glasshouse material yet the incubation period of the virus is decreased in tissue cultures.

Formation of stems both in callus tissue isolated from hypocotyl and in apical meristems culture of carnation plants (Dianthus caryophyllus L. ev. "Grenadin white, yellow, scarlet red, dark red and pink") was evokedin vitro using chemically defined medium. The rooted stems were transferred into pots and cultivated under natural conditions.

The development of excised flax embryos of different age was followed in nutrient media with different osmotic values. Sucrose media with the osmotic value 4.0 bar. (5%) sucrose were the most suitable for the cultivation of excised 7 and 14 days old flax embryos. Nutrient media with the osmotic potential 1.7 bar (2% sucrose) were optimal for 28 days old embryos. The most convenient osmotic potential for optimal root growth was 4.0 bar and for hypocotyls and stems 1.7 bar. High osmotic value of the cultivation media prevented the germination of the embryos and lower osmotic value promoted the germination. Mannitol, when compared with sucrose, inhibited the development and germination of the embryos. Different abnormalities often occurred on the media with mannitol. Agar media were superior to liquid media for the cultivation of explanted embryos.

The paper describes isolation and partial characterization of the tissue culture of the common spruce (Picea excelsaLink). The tissue culture was grown on the medium ofHarvey (1967) modified by increasing the concentration of 2,4-dichlorophenoxyacetic acid (2,4-D) to l mg l^-1 and by omitting the tyrosine. By selective 10-month subculturing the tissue culture was obtained possessing relatively stable properties and giving good yields of biomass. The tissue of the callus was of yellowish colour, compact and homogenous. The obtained tissue culture was characterized by its growth curve and by following the O₂ consumption during the growth.

Indole-3-acetic acid (IAA-1¹⁴C, IAA-2¹⁴C) and gamma-aminobutyric acid labelled with¹⁴C were applied in lanoline to the surface of intact seeds or inserted into seeds of growing apple fruitlets or to the cut surface of the pericarp. Their translocation in trees was checked by means of autoradiography or by a low background Geiger-Müller counter. Auxin applied to the top of intact seeds, or inserted into the seeds was translocated and distributed within the pericarp, spur tissues and shoots below. The translocation of gamma-aminobutyric acid from seeds suggests that the capacity of apple seeds for extensive interchange with the surrounding tissues of the fruit and the spur is more general than suspected. A much poorer or no translocation to the spur was found when radioactive compounds were applied to the cut surface of the pericarp, while the seeds were left untouched. The results suggest two mechanisms of metabolite translocation in the apple fruit: two-directional for seeds and one-directional for the pericarp.

The photosynthetic rate in leaf discs (P_LD) ofPrunus laurocerasus L. plants taken up from leaves of various ages was measured under constant temperature (20±0.5°C) CO₂ concentration in air (0.03%) complete water saturation and irradiance (71 W m² PhAR). TheP_LD is the highest in mature leaves of the current year. The extent of depression in the second and further years depends on the degree of habitat shading. In a slightly shaded habitat (60 to 73% daily sum of photosynthetically active radiation-PhAR) it decreases by almost 50% in the second year. In a deeply shaded habitat (22.5-28.2% daily sum PhAR) the depression amounts to 31.7% in the second year in the third and fourth years to 61.7 and 73.2% respectively.

Growth of primary (cv. Wisconsin 38) and long-term (cv. Virginia Bright Italia) tissue cultures obtained fromNicotiana tabacum L. pith was affected by exposure to a single dose of gamma-radiation ranging from 1 to 150 krad. The inhibitory effect was proportional to the applied dose. Changes in the degree of inhibition during the subculture interval were ascertained by quantitative evaluation of the growth response. Primary cultures proved to be several times more radiosensitive than long-term cultures, the capacity to recover from radiation damage of the cultures participating in the resulting manifestation of the effect. The possible reasons for these differences are discussed.

The substrate specificity of apple seeds phenol oxidases was investigated in polyacrylamide gel electropherograms. The nonspecifico-diphenol oxidases were distinguished as well as fractions showing the specificity for some structural elements of substrate molecule. The role of particular oxidases in phloridzin transformations in apple seed was discussed.

"Euonymus mosaic virus", purified from cucumber cotyledons by the differential and density-gradient centrifugation, shows typical nucleoprotein absorption spectrum. Electron microscopy reveals isometric virus particles of about 37 nm diameter. No reaction of purified "Euonymus mosaic virus" was observed with antisera against a raspberry ringspot virus, tobacco ringspot virus, cherry leaf roll virus, strawberry latent ringspot virus, tomato ringspot virus, elm mosaic virus, arabis mosaic virus, tomato bushy stunt virus and watermelon mosaic virus.

Third internodes or whole stems of 7-days old etiolated pea plants were extracted and the content of gibberellin-like substances and inhibitors has been determined. Extracts were found to contain four or five different gibberellin-like substances, some of which are chromatographically similar to GA₃. The content of gibberellins has been high in young internodes and decreased along with the internodes elongation. Brief red light irradiation brings about quantitative changes in gibberellin content, depending also on the length of internodes. The extracts contain acidic and neutral inhibitors which interfere with the response to GA₃. The content of the inhibitors does not seem to be affected by the ageing of internodes or by the light treatment.

An open system has been designed which enables a simple and rapid manual regulation of the CO₂ concentration and absolute humidity in the assimilation chamber according to the actual CO₂ and water vapour exchange rates, respectively. This ensures a constant effective CO₂ concentration and humidity irrespective of the gas exchange of the leaves. The installation is supplemented with an irradiation system providing irradiance at the leaf level up to 3 200 μeinstein m^-2s^-1 (400-700 nm),i. e. ca. 675 W m^-2.

On the roots of the unchilled apple seedlings treated with morphactin many deformed adventitious shoots were formed, whereas when the roots were dipped in the mixture of morphactin and NAA more adventitious roots were produced than when only NAA was used. The growth of these lateral roots was greatly inhibited. Similar interaction of NAA with morphactin in the development of roots was obtained when the chilled seedlings were treated with these growth regulators before the buds developed. The sections of the roots from all the treatments were made and the anatomy studied.