StrainsAspergillus amstelodami No. 5,A. chevalieri A 24 andA. ruber No. 71 were maintained for 21 generations on wort and on Czapek's medium with 20% sucrose by means of monoconidial isolation. A gradual increase in conidium formation was observed which was different on the two media. No decrease in the formation of perithecia or their disappearance could be observed. In strainsA. amstelodami No. 5 on wort andA. ruber No. 71 on Czapek's medium with sucrose, three morphological changes could be detected, characterized first of all by retarded growth and delayed differentiation during the first days of incubation and by reversibility to the original phenotype in some colonies during subsequent generations.A. chevalieri A 21 displayed two different phenotypic changes on wort medium, the changes appearing to be characteristic and permanent. They are accompanied, in addition to other morphological features, by retarded growth and delayed differentiation during the first days of incubation.
The present results are compared with those ofJinks (1954, 1956) and the origin of the changes observed and the effect of media is discussed. As concerns the reversible changes it can be assumed that they are of extranuclear origin since it appears to be justified to rule out changes caused by the mutation of the genome and by segregation of nuclei due to heterokaryosis. With changes where no reversion can be observed the origin is not clear. Increased sporulation is ascribed to changes in the cytoplasm.

Proliferation of the cambium and parenchyma of branches from 34 tree species was studied by means of tissue culturesin vitro. The formation of callus tissue, the seasonal activity of cambium, the effects of indole-3-acetic acid on the reactivation of cambium and the polarity of callus formation were investigated.
Various tree species are characterized by a different capacity for callus formation; in the majority of species, however, the reaction of cambium takes place in culturesin vitro. Some species produce callus from the cortex and the pith of branches and the lenticels simultaneously with the reactivation of cambium.
Growth of callus tissue was maximal in winter, adequate in spring before budding occurred and later decreased greatly. During the summer the growth-rates increased again and in the autumn were close to those encountered during the winter. Some species are characterized by a similarly intensive cambial proliferation throughout the whole year.
Indole-3-acetic acid (IAA) in the cultivation medium had various effects on the growth of callus tissue in the species examined. A series of species initiated meristematic foci in callus tissues that gave rise to roots (more frequently on media with added IAA) or to buds and stems.
The position of the sections in the medium (whether the apical end was placed upwards or downwards) had no great effect on the polarity of callus formation. Some species produced callus tissue at both ends of sections.

The previously found (Slavík, 1959) distribution pattern of osmotic pressure of cell sap in the area of the leaf blade of dicotyledonous type which is independent of the water balance and unchanged even with zero diffusion pressure deficit, was complemented by further data concerning the physiological heterogeneity of the adult leaf blade ofNicotiana sanderae hort. in relation to water relations and CO₂ exchange.
The transpiration rate from the intact leaf surface was found to be about 50 to 70 per cent lower in the apical part of the blade than in the basal part. The natural permanent water saturation deficit was found to be about 10 per cent lower in the apical part. The stomata density in tobacco as well as in sugar beet leaves were on an average 40 per cent lower in the apical part, their size being here 30 per cent higher. The relative index of the area of the stomata pores (density × square of the pore length) did not differ significantly in the two places. The photosynthetic rate (per area) in fully water saturated leaves was found to be 17 per cent lower in the apical part of the blade, the chlorophyll content (per unit area) being greater in the thicker apical part. Respiration rate measured manometrically as Q_O2 was significantly lower in the apical part, both when calculated according to area and to dry weight (12 per cent). Similar but much lower differences were found between the edge and the central part of the leaf blade.
This physiological heterogeneity and polarity of the leaf blade originating in the ontogenesis of its extension growth is causally based on the different relative hydration levels. Thus the study of various physiological processes in different parts of the leaf blade is suitable for the investigation of their relationship to different hydration levels.

Transpiration rates of leaf blades of irrigated and not irrigated spring wheat plants were studied in relation to the water content and growth changes in the test plants during their development. The applied irrigation stimulated the growth and slightly delayed the development of the test plants. It increased chiefly the water content and to a lesser degree the dry solid weight in the plant body. The quantitative and qualitative properties of the water content in the plant affected not only transpiration rates, but also the development of new and the dying off of old organs and tissues, especially of leaf blades. Transpiration rates in irrigated plants were markedly higher than in not irrigated plants. Mean transpiration rates of different leaf blades varied and were typical for each leaf blade. From the static aspect it was possible to express and even to explain some of the relationships and the heterogenity of the leaf blades on the same stem by the "Law of Zalensky". This involved mainly the mean values of growth characteristics and the investigated features of the water regime. On the other hand, from the dynamic viewpoint it was possible to divide the different leaf blades according to their transpiration changes into two groups. The first group includes the blades of the first to third leaf, the second group the blades of the fourth to sixth leaf and the ear. The capacity to control the water regime in the different blades is greatest at the stage of tillering, shooting and milk ripeness. During these developmental stages the marked decrease in transpiration, caused in the first place by a number of internal and not only external factors, was explained.

The work described here was carried out during the last three years mainly on the castle premises at Lužany near Přeštice (Hlávka's foundation). It dealt with the disease of the horse chestnut-tree (Aesculus hippocastanum L.). The symptoms and their development have also been observed at a number of other places. According to the classification ofBose (Wageningen) the symptoms belong to the groups of Colour changes (II), Necrosis (IV), Deformation (VII) and partly also Growth reduction (of fruits). We are dealing here with a disease that was described bySorauer andThomas 60 years ago as abiosis. Since some of the symptoms suggested a virus origin of the disease some diagnostic tests were carried out. The serological test was negative on account of the chemical composition of chestnut leaves which are not amenable to such tests. Grafting and inoculating tests on healthy seedlings were positive. Viral necrosis of the horse chestnut is a disease of the system which is not transferred by contact. It is readily transferred by grafting and inoculating. Some symptoms suggest that it can also partly be transferred by seeds.

The effect of photoperiodic inhibition on the course of development was demonstrated by changes in the length of the sheath and the lamina, the lamina being more affected than the sheath. In a number of variants with different initiation of photoperiodic inhibition, an elongation or shortening of the sheath and the lamina of the three top leaves was observed compared with corresponding control leaves. The shortening occurred in leaves which developed beyond the normal number of the original bracts. This was the case with variants with very early inhibitions. Variants with later inhibition had on the one hand abnormally reduced leaves with imperfectly developed spikes, on the other hand elongated leaves whose length resembled that of ontogenetically younger, lower leaves. The suitability of the morphology of leaves for the investigation of the course of plant development is discussed.

Při pěstování rostlin kukuřice ve sterilních kulturách je třeba obilky desinfi-kovat, aby se zniěily zárodky mikroorganismů. To snižuje jejich klíčivost, zpozdí růst a tvorbu chlorofylu během prvních několika týdnů vyvoje klíčních rost-linek. Nejde o specfflcké inhibice, nýbrž o vývojové opoždění neprojevující se ani v poměru dlouživého růstu a hromadění suŠiny. Opoždění je nejvě tší při po-užití roztoku sublimáta nebo ethanolu. Vhodnější je desinfekce roztokem chlor-aminu. Změny vyvolané tříhodinovým namáčením jsou vyrovnány během cca 3 tydnů, bězně užívaná sedmihodinová desinfekce vyvolává kromě silného sní-zeni klíčivosti (téměř ? 50 %) déle trvající, avšak nezásadní změny. Chloramin neovlivnil tvorbu pohlavních organů, intensità fotosynthesy byla úměrná množství chlorofylu. Desinfekce chloraminem lze tedy užít, aniž by se rostliny podstatně lišily od těch, které byly vypěstovány ze suchých obilek.

Analyses of free amino acids and amides in the axial parts of apple-trees with and without flower-bud initiation were carried out. The results obtained mostly on the basis of investigations carried out during a single vegetation season, indicate that the ratio and content of free amino acids and amides in the axial parts of apple-trees are influenced primarily by the growth of the axial parts and by nitrogen supply to the roots. These findings are in agreement with the results of Oland (1959). In fruit-bearing trees a high content of free amino acids and amides could be demonstrated, together with an increased ratio of soluble to insoluble nitrogenous compounds solely in the fruit-bearing new cluster bases (bourses). This finding is in accord with the results of Haeley and co-workers (1942). No apparent relationship could be established between the content and ratio of free amino acids and amides, and the ratio between soluble and insoluble nitrogen compounds on the one hand, and flower-bud initiation, on the other. The investigation is being continued.

The sequence of intensities with which pollen tubes utilize tested sugars from their 0.3 M solutions, is the following: sucrose >glucose >invert sugar > >fructose. The same sequence is maintained in sugar-agar media with the exception of the first two hours of incubation when sucrose, glucose and fructose are all utilized at a practically equal rate. During this period no pollen tubes were formed in the presence of fructose, in common with the sugar-free control, while in the presence of sucrose they reached a length of up to 450 µ. If sucrose was used as carrier for radioactive sugars, fructose-¹⁴C was utilized up to 12 times and glucose-¹⁴C as much as 6 times more actively than sucrose-¹⁴C. When sucrose + glucose or sucrose + fructose (in molar ratio 1 : 1) were used the pollen tubes utilized sucrose-¹⁴C at a slower rate than the corresponding monosaccharide and also at a slower rate than observed with sucrose alone. When glucose or fructose was used as carrier for sucrose-¹⁴C . the carbon dioxide-¹⁴C production by the pollen tubes was (during several time intervals of the experiment) several tens per cent higher than when sucrose served as carrier. Fructose is utilized preferentially from a medium with invert sugar.
It thus appears that the capacity of the pollen enzymic systems for incorporating the sugars tested into their respiratory pathways is as follows: fructose >glucose > sucrose, this sequence being the opposite to that found for the intensity of their growth effect and to that established for the rate of their utilization, unless present in combination. The specific growth effect of sucrose cannot thus be due primarily to the rate of its absorption or to the intensty of its utilization. The rapid rate of utilization of sucrose alone is due to the more intense growth in the presence of sucrose. The results obtained further suggest that sucrose is utilized above all via its inversion when the fructose component is respired preferentially.

The present investigations were designed to explain the physiological causes of the increase in metabolism and growth in the shrubRhus aromatica L. after pruning. The determination of the concentration of the different forms of nitrogen compounds, of sugars, organic acids, phosphorus and also of the dry weight of the leaves from the pruned and from the control plants at different times during 24 hours, showed that the positive influence of the pruning on plants is due to the increase of the amplitude and of the synthesis and transport of organic substances from the leaves as well as of the transport of the minerals and water into the leaves.

Experiments on the effect of sodium humate on the swelling and germination of the winter wheat Pyšelka (Triticum vulgare Vill.) and on the changes in respiration intensity of swelling seeds during the first 24 hours of swelling, are described.
It was found that sodium humate at a concentration of 100 mg./l. accelerates the uptake of water by swelling seeds during the initial phase of swelling. The fact that the seeds take up a sufficient amount of water sooner makes it possible for the activation of enzyme systems which ensure normal germination to take place, thereby bringing about an increase in respiration intensity. The energy released during respiration is then utilized for more rapid growth of the embryo which is morphologically reflected in the rate of germination.

The cluster bases (bourses) in each case had a higher content of total nitrogen and both absolute and relative soluble organic nitrogen than the new secondary growth of cluster bases on trees both with fruit and without fruit than new spurs on trees with fruit. This higher content of total and soluble nitrogen is primarily a feature of the organ and has no connection with the initiation of flower buds. The secondary growth of cluster bases on the trees with fruit never had a significantly higher content of soluble nitrogen than the new secondary growth of cluster bases and new growth of spurs on trees without fruit. In all apple varieties observed the same qualitative pattern of free amino acids and amides was determined and a similar ratio of free amino acids and amides in the corresponding axial parts. The highest amount of free amino acids and amides-especially asparagine and arginine-was determined in the cluster bases. Arginine was accumulated in large quantities in the cluster bases much earlier than in the secondary growth of cluster bases or in the new growth of spurs. An accumulation of arginine and asparagine occurred in the cluster bases even when the supply of nitrogen was insufficient, in the secondary growths of cluster bases, however, their content was very low during nitrogen deficiency. The content of glutamine and sometimes threonine in cluster bases with fruit was also considerably increased. There was more glutamic acid, glutamine and sometimes threonine too in younger axils than in older ones already lignified.
From results given in this work it can be concluded that there is no obvious relation between the content and proportion of soluble and insoluble nitrogen in the spurs of apple trees on the one hand and the initiating of flower buds on the other. Neither was any obvious relation determined between the content of free amino acids and amides in the axillary parts of apple trees under observation and the initiating of flower buds.

An investigation was made as to whether the cultivation conditions of algae affect their respiratory metabolism. Chlorella pyrenoidosa (82), Scenedesmus obliquus (125) and Euglena gracilis (259) were cultivated both in a static and shaken culture.
It was found that shaking considerably affects the respiratory metabolism of algae. The shaken cultures, in contrast to the static ones, display a higher O₂ consumption and have mostly a different RQ. It is possible that the differences observed are due to accelerated development and ageing of the shaken cultures.
It thus appears that shaking is an important factor in cultivation which must be taken into account during growth of experimental material. The values of RQ found here to be about 1-3 point to the fact that anaerobic glycolytic processes can proceed even under fully aerobic conditions. The culture of Scenedesmus obliquus (125) appears to have a less adaptable metabolism and does not respond to environmental changes as readily as Euglena gracilis or Chlorella pyrenoidosa.

It was the objective of the present communication to establish the effect of short-term aeration with air alone or air enriched with 5% carbon dioxide on growth and oxidative metabolism of Chlorella pyrenoidosa. An organic medium was used to permit the investigation of the effect of aeration (one hour a day) both under illumination and in continual darkness.
Short-term aeration with air either alone or enriched with carbon dioxide increases dry-weight production both in the light and darkness. We are thus not dealing here with a mere effect on photosynthesis. This treatment affects the oxidative metabolism of the alga: oxygen uptake was always higher in those cultures which were more aerobic during cultivation (aerated cultures in the dark and non-aerated, or only with pure air cultures in light). Cultures in the individual variants display different endogenous respiration when measured manometrically.

Photoperiodic experiments with the spring wheat Niva were undertaken to investigate the course of photoperiodic sensitivity and localization of the dhotoperiodic reaction in the ontogeny of plants. The long-day plant used, however, was not amenable to detecting a period during which a shortened day would be completely devoid of effect on the rate of development. Some data indicate, however, that a period of increased photoperiodic sensitivity can be defined which would correspond to the period of photoperiodic reaction of short-day plants. The results also seem to indicate that this period does not terminate abruptly but gradually passes over into the ensuing period when the day length affects the rate of development solely through photosynthesis. This effect is well marked when such indicators as the shoot apex development and earing are employed. The existence of this transition period at the end of the period of increased photoperiodic sensitivity and its connection with the shoot apex phase from initiation of spikelets to initiation of stamens must be verified by a long-term experiment under strictly controled conditions.
Among the criteria used to examine the course of photoperiodic sensitivity earing appeared to be most suitable as it yielded curves with definite, more or less marked breaks; the investigation of abnormities (in a classical arrangement), too, proved to be of value, as they indicate interference with the relationship between growth and development. Orientation data were also obtained by measuring plant size in a classical arrangement of the experiment. Analyses of the developmental phase of the shoot apex proved to be of least value in the experiments described here.

The growth of pollen tubes evokes changes in the level of free amino-acids in the style. This has been demonstrated in the cases of alanine, valine, leucine-isoleucine, serine, threonine, γ-aminobutyric acid, asparagine, glutamic acid and proline. These changes take place mainly in the parts of the style where the pollen tubes are present.
The most marked changes are an increase in the level of γ-aminobutyric acid and alanine and a decrease in glutamic acid. The intensity of these processes is much greater following compatible pollination than in the case of incompatible autogamy. On the assumption that the main course of γ-aminobutyric acid and alanine katabolism takes place by transamination with α-ketoglutaric acid, the basic nature of the above changes is explained as being due to a relative deficiency of the latter acid.
Alongside a reduction in the level of sugars an accumulation of asparagine takes place in pollinated styles. The rise in its level is considerably more rapid in cross-pollinated than in self-pollinated styles. If accumulation of asparagine is a result of more intensive consumption of proteins during respiration when there is a scarcity of sugars, it follows from the above results as from previous work (TUPý 1961), that pollen tubes use substrates from the style tissues for respiration and that this process is limited in the case of incompatible inhibition.
At the time when the pollen tubes are growing through the styles, the levels of γ-aminobutyric acid and alanine are already rising in the ovaries of pollinated flowers. This increase is quantitatively in direct ratio to the rate of pollen tube growth, which depends on the compatible or incompatible character of the pollination.

1. Photoperiodic experiments with the effect of short day during vernalization of winter wheat under field conditions have shown that the short day enhances development if applied during vernalization. Short day applied after vernalization prolonged the development.
2. At low intensity artificial illumination and under optimal vernalization temperatures vernalization proceeds the faster the longer the illumination. On increasing illumination intensity differences between the effect of short and long day are obliterated. Vernalization in the dark takes place only if saccharides are added.
3. It is assumed that even in green plants the accumulation of a certain amount of ergastic material, particularly saccharides, represents one of the conditions of vernalization. This accumulation may be achieved by longer illumination (under conditions of vernalization temperature and low illumination intensity), i.e. by a direct photosynthetic effect, or else by short day (under field conditions) causing a specific, photoperiodically controlled growth reaction which inhibits growth. When vernalization proceeds in the dark saccharides must be supplied.

Antagonism of three saprophytes to the pathogen,Rhizoctonia solani was studied in plate cultures under different conditions of temperature, pH, and nutrition. The antagonistsTrichoderma viride andChaetomium cochlioides were found more effective in the inhibition of the growth ofR. solani at temperatures 25 and 20° and this conforms to their growth-temperature relationship.T. viride was found more effective in acid media as reported by others, whereas other antagonists and especiallyC. cochlioides was more effective in the alkaline medium. Hence the suggestion is made that soil amendments increasing the activity ofC. cochlioides might be a good control measure against the pathogen in alkaline soils.
The most interesting result of the investigation is that, contrary to the previous reports,R. solani appeared to be more cellulolytic thanT. viride andC. cochlioides and this result was unaffected by the use of NH₄C1 as N-source.

Humus acid (Humussäure Riedel de Haen AG. Seelze Hannover) in 0.01% concentration increases the respiration intensity of plant roots grown in water cultures both as regards O₂ consumption and CO₂ production, while RQ (CO₂:O₂) is only very slightly increased. The plants used in these experiments were the winter wheat Pyšelka (Triticum vulgare Vill.), maize Zaj íček's "Český koňský zub" (Zea mays L.) and the gourd Veltrusská velkoplodá (Cucurbita maxima L.). O₂ consumption and CO₂ production were determined on separated root tips by the direct Warburg method. It was found that the effect of humus acid is not only to increase respiration intensity in the roots of the experimental plants, but also their lengths and dry weights (for all experimental plants); for maize and gourd the dry weights of overground parts were also increased, which indicates that increased respiration intensity was linked with more intensive growth of the plants.

1. It was found that fluoride has a more pronounced inhibitory effect on the respiration of wheat leaves in plants grown in a solution of gibberellic acid than on that of control plants grown in water, during the entire development of the first leaf.
2. Respiration is markedly inhibited even in old leaves of gibberellintreated plants while the respiration of equally old control plants is stimulated by fluoride by 10-100%.
3. It is assumed that the shift in the equilibrium of respiratory pathways to glycolysis, as is indicated by respiration experiments, is associated with the growth effect of gibberellic acid.

The paper describes a new strain of tobacco mosaic virus which has been named S-strain of TMV because of its characteristic stripe symptoms. The Al-strain of tobacco mosaic virus was used as the initial material.
In contrast to methods used hitherto the S-strain was obtained by interfering with the metabolism of the host plant by a change in the environment. (SvobodovÁ 1954, 1958). The usual hosts of tobacco mosaic virus were used, chiefly tobacco and tomato plants. These plants were cultivated under aseptic conditions on an agar medium in Erlenmeyer flasks with a reduced amount of nutrients, a shortened period of illumination and a limited air supply, so that they were stunted. Following the passage of the initial Al-strain of TMV through these dwarfed plants changes in symptoms appeared, which became apparent only after further passages through plants grown under normal conditions in a glass house in garden soil, where the virus once again had normal conditions for reproduction. Of the new symptoms obtained, only the most striking were further studied (the symptoms of S-strain). By means of alternating of the passage of the Al-strain of TMV from normal-to dwarfed-to normal plants grown under artificial nutrient conditions, i. e. a twice or thrice repeated sudden change of environment, the new strain (S-strain) was obtained five times in all and at different times of the year. From the symptomatic point of view no differences were found in the different repetitions of this change. The results were also the same for material from tomato plants and from tobacco of the Samsun variety.
The origin of the new strain was not caused only by the stuntedness of the host plants. It was also necessary to influence its metabolism by an abnormal environment (particularly insufficient air) in the Erlenmeyer flask before and after inoculation.
Following the reverse passage of the S-strain from plants grown normally in a glass house to dwarfed plants in an artificial environment no further changes occurred. Neither did the passage to ten other hosts grown normally on garden soil and in artificial nutrient produce any further change in symptoms. The S-strain has been maintained by a succession of continuous passages throughNicotiana tabacum Samsun for six years, and each year mass inoculation of a large number of plants is carried out. We therefore now consider the change to be permanent.
Indirect influencing of the virus through a change in the metabolism of the host plant sufficed for the induction of the new strain. Its symptoms appeared only after passage through normal unaffected plants, where the virus reproduction was not inhibited by the retarded growth of the host plant. There is a certain similarity in the emergence of the S-strain and the TM44-stram, obtained byPfanchuch et al., with X-ray irradiation. However, the initial material was the ordinary green strain of TMV.
The biological, chemical and other characteristics ascertained for S-strain and a comparison of these with the characteristics of the initial Al-strain and the ordinary green strain of TMV will be published later.

Root formation was studied in cuttings from tomato plants infected with stolbur and Czechoslovak type II potato witches' broom viruses. A highly significant difference in root formation was always found in plants with clear-cut disease symptoms. Potato witches' broom virus inhibited the root growth more than stolbur. In all cases, diseased plants showed a greater variability in the weights of roots than healthy controls.

1. The symptoms caused by the S-strain(Svobodová 1954, 1958, 1959) were described for ten hosts and compared with those caused by the Al-strain and the ordinary green strain of the tobacco mosaic virus. In all the host plants tested the S-strain produces symptoms different from those caused by other strains.
2. A comparison of the incubation period and the effect on growth ofNicotiana tabacum Samsun, the behaviour onN. rustica and quantitative tests onN. glutinosa showed that the S-strain is the least pathogenic of all the strains compared.
3. Results of biological tests show the S-strain to be most similar to the ordinary green strain of tobacco mosaic virus, only serological and cross-protection tests indicate a closer relationship to the Al-strain, from which it developed.
4. The behaviour of the S-strain of TMV in expressed sap is similar to the behaviour of the ordinary green strain and of the Al-strain. The range of hosts for all three strains is also the same.Physalis alkekengi andP. Franchetti are to a certain extent differential hosts.
Thus biological tests show that the S-strain is a new strain of tobacco mosaic virus.

1. Attention is called to the possibility of using resoroin blue for the staining of pollen tubes within the style tissue and the method of staining is described.
2. In pollen tubes, the growth of which is inhibited due to incompatibility, there is at least twice the amount of callose relatively to their length as there is in normally growing compatible tubes. In apple this is primarily due to the greater length of the callose plugs, in tobacco also to their greater density.
3. The regularity of the formation of callose in pollen tubes increases with the rate of their growth.
4. It is suggested that the physiological basis of callose formation consists in the limited capacity of pollen tubes to use the pyran components of metabolized saccharose in the process of respiration.

Hemp (Cannabis sativa L.) was sown at intervals from November to August. For each sowing the time of flowering was recorded for male and female plants separately. Male plants usually flowered earlier than female. When the period of daylight exceeds 14 hours, that is when the days are lengthening in April, the female plants stop flowering and continue their vegetative growth. They start flowering again when the days are shortening considerably, in August, when the daylight period is about 15 hours. The male plants flower even when the day is longer than 14 hours.
In experiments during which the plants were shaded it was found that reduction of light intensity leads to an increase in the number of female plants, particularly if shading is carried out in the early stages of the plant's development.
The occurrence of intersexual plants was observed only during the short day period (11 to 13 hours), when they composed 22-30% of the total. When the day exceeds 13 hours intersexual plants no longer develop.
The grafting of plants of varying sex did not produce any sexual change-probably due to the fact that the period of vegetative approximation was short.

The work presented in this paper was a study of the influence of different isolated humus substances when applied to the overground parts of plants by spraying on the leaves. The humus components employed showed varying effects on growth, respiration and chlorophyll content inBegonia semperflorens Link et Otto. The result of the physiological changes is reflected in morphological changes of the overground parts and particularly in the structure of the root system. Fulvic acids were found to be the most effective of the humus components when sprayed on leaves.

The authors studied the effect of the application of humus substances to the leaves ofBegonia semperflorens Link etOtto. For spraying they ušed a dialysed extract of garden soil containing sodium humate with admixture of fulvic acid in total concentration of 300 mg/l. Doses of 2 ml. were applied twice a week during the period of the main growth phase.
It was found that humus substances applied to the leaves cause a leng-thening of plant organs and increase of their fresh and dry weights. The chloro-phyll content and the amount of expired carbon dioxide are increased. The final result depends on the time when spraying was carried out and on the concentration used. It can be assumed that these effects are the result of direct influence by the humus substances and are not due to the action of stimulated soil or root microflora nor to improvement of the physicochemical character of the soil environment.
In conclusion we may say that humus substances applied to the leaves cause lengthening of the plant organs and increase in their fresh and dry weights. Chlorophyll content and the amount of expired carbon dioxide are also increased. The final effeet depends on the period of spraying and on the concentration used. In view of the fact that these effects do not differ from the effects caused by humus substances given as a part of root nutrition, we may assume that they are the result of direct action of humus substances and not of the action of stimulated soil or root microflora, nor to the improve-ment of physical or physico-chemical character of the soil environment.
A prerequisite for the practical utilization of humus sprays is, however, the extension of experiments to a greaternumber of plant species, the determination of their sensitivity, suitable concentrations of the solutions and the most suitable time of application.

This paper presents a summary of new evidence for regarding sterility and dwarfing of oats (OSDV) as a virus disease. Brief references are also made to the identification of a further virus in Czechoslovakia-the wheat striate virus (WSV). Both viruses are transmitted by the leafhopperCalligypona pellucida F. The wheat striate virus differs from the oat sterile-dwarf virus in that it can be passed transovarially by the infected females of the vector to their progeny. This characteristic, which made it possible for the two viruses to be separated from each other, was demonstrated for the first time for pathogenic viruses on the European continent in this case. OSDV can be transmitted by leafhopper larvae and adults. The time during which OSDV circulates in the vector's body is very variable; it is usually three to four weeks. The incubation period of OSDV was three to four weeks for oats, four to seven weeks for wheat and barley; rye only showed retarded growth after four weeks. For infection to take place it was necessary for the vector to remain for a minimum of half-an-hour on the test plant; 100% infection was obtained when the vector remained on the plant for three days. The injury inflicted by OSDV on the host does not increase proportionately either with the duration of the feeding period or with an increase in the number of vectors on the plant. Concentrated extracts of the crushed bodies of infectious leafhoppers produced no symptoms of disease, when rubbed or injected into oat plants. Nor were attempts to transfer OSDV and WSV through soil or dodder successful. OSDV was, however, transferred by grafting. Both viruses gave rise to characteristic symptoms inAvena fatua L. andPoa annua L. These findings are discussed from the etiological point of view.