In a potted experiment the influence of foliar application of triacontanol (TRIA) at the concentrations of 0.01; 0.10; 1.00 mg dm -3 , and Asahi SL at the concentrations of 0.1; 0.2; 0.3% on the growth and yielding of plants was studied. Electrolyte leakage, water saturation deficit, contents of proline and chlorophyll a + b in leaves, as well as the maximum quantum efficiency of chlorophyll (F v /F m ) and gas exchange in plants which were treated for five days in temperatures of 15/7°C (day/night) were also examined.The achieved results showed that periodic chilling decreased the value of all the analysed parameters of the plants to a significant degree, with the exception of electrolyte leakage, water saturation deficit and proline content, whose values under these conditions increased. Triacontanol and Asahi SL favourably influenced both the

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The effect of exogenous spermidine (0; 1 and 2 mmol·dm^-3) on cucumber plant subjected lo seven day drought (30% f.w.c.) were studied. Growth rate of plants, gas exchange, chlorophyll fluorescence, water saturation deficit in tissue (WSD). leakage electrolytes (E^l as well as the content of free proline were determined. The results showed that drought inhibited growth and gas exchange, decreased the potential efficiency of PSII (F^v/F^m) but increased the value of WSD, E^L and the level of free proline in tissue. The spermidine treatment of plants immediately before drought influenced the decrease concentration of free proline, water deficit and leakage of electrolytes but the increase of stomatal conductance (g^s), intensity of photosynthesis (Pⁿ ) and transpiration (E). Greater change on the course of primary photosynthetic reactions in PSII (F^v/F^m., ΦPSII, qP, qN) were not detected. The autors concluded, that in drought. conditions exogenous speimidine together with proline induced by stress, contribute to increase of water content in tissue and maintenance of the enzymatic activity of cells as well as they guaIantee the integrity of cell membranes. Profitable effect of spermidine on the condition of cucumber in drought period shorted the time necessary for plants to come back to level of control treatment.

The reaction of the rape and corn plants on the nitrogen applied in the form NO₃^- or NH₄⁺ was studied under the controlled conditions. The ammonium ions with rape markedly lowered the growth rate, the intensity of photosynthesis and biomass yield, with relation to the plants fertilized with nitrates. With corn the effect of both N-forms was similar and positive. The biomass of the rape using NH₄⁺, with relation to the plants fertilized with NO₃^- showed lower content of total N, and protein N, as well as markedly higher content of amino-acids of primary protein synthesis and their amides and free ammonium ions. Yet, the corn utilizing N-NH₄⁺ showed, as compared with the plants fertilized with NO₃^-, higher content of all studied organic N fractions. with similar content of free ammonium ions. This paper presents the thesis that the cause of the growth inhibition of rape fertilized with ammonium is low, as compared with corn, assimilation of NH₄⁺ ions drawn in the roots of this plant

Measurements were carried out of the assimilation area, NAR value, the crop growth rate (C) and of the yield of roots and leaves of sugar beet plants in a production field during two successive vegetation years. An interdependence was found between the formation of the assimilation area in the canopy and the final yield of biomass. The assimilation area depended mainly on the date of sowing. In 1975, the sowing was earlier by 15 days, amid this resulted in a much more favourable LAI and in a higher yield of biomass. During both vegetation years, a violent decrease of the crop growth rate was observed at the end of August and at the beginning of September. This may be due to an unfavourable change in the ratio of the area of younger, photosynthetically active leaves to older, less active leaves and also to the increased participation of the loss of the assimilates resulting from stronger respiration of the fast growing roots while the photosynthesis of the whole plants decreases.