Net photosynthetic (P_N) and dark respiration (R_D) rate, stomatal (rs') and internal (ri') resistances to carbon dioxide were measured by gas exchange methods on leaves of different ages, expressed in leaf plastochron index units (LPI) for a fast growing poplar cultivar Unal 2. Although the optimal leaf age differs slightly for the different gas exchange parameters, leaf ontogeny is reflected in the same way in these different parameters. MaximalP_N and minimalrs' and ri' values were found at LPI between 6 and 10. Chlorophyll concentrations were lowest at LPI lower than 10 although an increase in two steps was found, when leaf age increases up to maturity.

Roots were excised from barley embryos cultivated in the complete liquid nutrient solution and cultivated in the same nutrient solution separately. The excised roots continued their growth but a progressive decrease in the growth rate was observed. There was a considerable short-term drop of the mitotic activity immediately after excision, which was followed by a compensatory increase and then equilibrium was reached 12 h after excision. During the next at least three days, the mitotic index of isolated barley roots varied between 5-6.5%, which is slightly lower than the mitotic index of the root meristems of isolated barley embryos under identical conditions. The mitotic cycle index of isolated barley roots and the size of the root meristem later decreased gradually.

Anomocytic stomata and stomata with single subsidiary cells are commonly observed Sometimes a stoma appears anisocytic. Double cytoplasmic connections between nearby stomata and division of guard cells with persistent or degenerating nuclei are seen in GA. One or more divisions of guard cells, displaced guard cells and single guard cells with or without pore are noticed in SUC. Formation of single guard cells is a common feature in TIBA. Paracytic stomata, one and a half stomata and persistent stomatal initials are seen in SUL. COUM seems to be not inhibitory inCucumis sativus. In COL stomata with unequal guard cells, unequal stomatal cells with thickening in between but without intervening pore, stoma with double pores, persistent stomatal initials which may be solitary or in groups with varying shapes and with one or two nuclei of different shapes are noticed. The growth regulators affect the frequency of stomata, epidermal cells; stomatal index; size of guard and epidermal cells.

The paper gives more detailed characteristics of Arabis mosaic virus (AMV) and tomato bushy stunt virus (TBSV) isolated from lilac, the latter being identified in lilac (from plants suffering from yellow ring disease) for the first time. The isolate of TBSV from lilac, from which an antiserum with a titre of 1024 was prepared, is closely related to the artichoke strain. Information is given about two types of ringspot disease and about chlorotic ringspot of lilac. Whereas in the leaves of lilac suffering from ringspot disease (of ring mosaic type) the presence of AMV was demonstrated, the sap transmission from the leaves diseased with ringspot of linepattern (and wave-like mosaic) type failed; from the leaves affected by chlorotic ringspot a mixture of AMV and cherry leaf roll virus was identified. In addition, the polyetiological nature of "spring" mosaic and necrotic mosaic of lilac, in which bacteriumPseudomonas syringaevan Hall, was found is dealt with. The TBSV was also identified in the isolate of necrotic mosaic.Additional index words: Lilac ringspot, chlorotic ringspot, yellow ring, "spring" mosaic, necrotic mosaic, cherry leaf roll virus,Pseudomonas syringaevan Hall.

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.

Using starch gel electrophoresis, a group of anodic isoperoxidases which is revealed byo-dianisidine (not by guaïcol) in the soluble fraction of roots proteins from lentil, pea, sugarbeet and maize is never found in corresponding extracts from stems. These root specific peroxidases do not show IAA-oxidase activity as revealed byp-dimethylaminocinnamaldehyde on the gels. They could not serve as a rhizogenesis index since they do not appear from the early beginning of root growth.

The roots ofAllium cepa L. were treated with water solutions of cyanein and griseofulvin for 24 and 48 h respectively, thereafter cultured for 48 h in the medium without the antibiotics, and the reversibility of the inhibition caused by the antibiotics was evaluated. Changes in the mitotic index of meristematic cells were followed in squash preparations of root apices. In addition to the cytologic observations, the differentiation of the primary meristem was followed in longitudinal sections. After the treatment with reversible doses of cyanein and griseofulvin respectively, differences were found in both the effects of the antibiotics during the treatment and the restoration of the inhibited processes after the treatment. In the cells treated with cyanein the restoration of mitotic activity was instantaneous but less intensive and in|complete especially in the case of the 48 h treatment. After the treatment with griseofulvin which temporarily interfered also with the differentiation of the primary meristem, the restoration of the inhibited processes was delayed but intensive after both application times, 48 h after the treatment no symptoms of the preceding inhibition could be observed.

Starch degradation inNicotiana tabacum cv. Samsun infected with PVY was studied with respect to the formation of Glc-6-P which serves as a starting substrate for glycolysis and pentosephosphate cycle. Enhanced activity of these two metabolic pathways at the time of maximal reproduction of the virus requires an increased content of this substrate which is probably produced mainly by the hexokinases. The results of this paper indicate that Gle-1-P, synthesized during starch degradation, is not the main intermediate enabling an enhanced activity of the pentosephosphate cycle, because despite a high starch content in the tissues only a decreased amylophosphorylase activity was found. However, an appreciable amount of Glc-6-P at the time of maximal reproduction of the virus results from enhanced phosphoglucomutase activity.
As there is not enough Gle-1-P for an enhanced activity of this enzyme due to the lowered activity of amylophosphorylase and because its curve resembles activity curves of the hexokinases (published in the previous paper), this result could be explained by the presence of galactose and by the presence of an enzyme system which would be able to metabolize it to Gle-1-P.Additional index words: Nicotiana tabacum, respiration, glycolysis, pentosephosphate cycle.

The association between latex RNA and latex production was examined using MAK column chromatography techniques. In young untapped trees the introduction of tapping or the treatment of bark with growth regulators resulted in an increase of RNA level and of rRNA/tRNA ratio in the latex. In regularly tapped trees an increase in rRNA but not in tRNA was brought about by increasing the tapping frequency. Treatment with growth regulators had the same effect but essentially only through the related enhancement of latex export from latex vessels. During latex flow, the highest RNA level was registered in latex fractions originating from the most heavily drained areas of bark. Using³²P labeling, evidence was obtained that the export of latex results in an enhancement of rRNA migration into the inner latex containing space of the vessels. This is considered as the reason of the generally observed association of high RNA level and of high rRNA/tRNA ratio with high latex yield. It is proposed that in controlling the RNA level and RNA proportions in the latex an important role is played by changes in turgor pressure associated with the loss of latex which may influence the export of RNA from the nucleus through related induction of pressure disequilibrium between the nucleoplasm and the latex cytoplasm.

Leaf angles, frequency distribution of leaf area inclinations, leaf area index, amount of intercepted radiation, biological, vegetative and grain yields and grain yield proportion of biological yield were determined in maize stands of two population densities, 55 555 plants ha^-1 (S₁), and 80 000 plants ha^-1 (S₂). Also the effect of the artificial change of leaf angle upon these indices was studied. We classified normal maize stand (N) as the interstage between a planophile and a plagiophile type of canopy, that with artificially changed leaf angle (V) as an erectophile type of canopy. The relative interception of the incoming radiation in the variantsV S₁ andV S₂ was lower than in the variantsN S₁ andN S₂. The variantsV in comparison with variants N increased grain yield and biological yield.

A study was performed on the effect of various concentrations of IAA, 2,3,6-triiodobenzoic acid, and maleic hydrazide, supplied to Richter's nutrient solution, on growth of pea plants in water cultures. After a 18-day cultivation growth was evaluated and in the plants gathered the content of total N, P, K, and Ca was estimated.
Growth of experimental plants (as evaluated from fresh and dry weight) was affected by all three regulators in dependence on the concentration used. It was stimulated by lower concentrations and inhibited by higher, the production of both fresh and dry weight of the root system being stimulated by all IAA concentrations used.
The ratio of root dry weight to that of the entire plant was markedly increased after application of IAA and 2,3,5-triiodobenzoic acid, whereas when applying maleic hydrazide it was only slightly increased in comparison with control.
Stimulation or inhibition of growth induced by IAA treatment was accompanied by an accordingly increased or decreased accumulation of N, P, K, and Ca. Thus their utilization did not change in comparison with control. On the other hand, both inhibitory and stimulatory effects of 2,3,5-triiodobenzoic acid and maleic hydrazide on growth were associated with a relatively lower accumulation of the elements in question, resulting in an increased utilization.
The distribution index of N, P, K, and Ca decreased with increasing concentrations of IAA, 2,3,5-triiodobenzoic acid and maleic hydrazide. Only the highest 2,3,5-triiodobenzoic acid and maleic hydrazide concentrations used brought about a more marked increase in the distribution index of potassium, simultaneously with a marked decrease in the distribution index of calcium.

Decreased accumulation of elements, particularly of nitrogen, had in dense stand a negative influence on the plants, in spite of the supply of fresh solution and the control of the concentration of nutrients in the pots. The fresh weight and the dry matter of one plant were reduced substantially with rising stand density (from 5 to 10, 20, 40 and 80 plants per 450 sq. cm); the RGR value, the relative absorption rate I_M, the content of all tested elements calculated per one plant, the chlorophyll content in the overground parts of one plant, and the distribution index decrease. Qualitatively the same influence is caused by deficiency of nutrients. Plant dying and self-thinning of the culture occurred in denser stand in the course of cultivation. The root-weight ratio rose with stand densification, particularly at the end of the experiment. The net assimilation rate (NAR) related to chlorophyll dropped with stand density; NAR at density "80" rose slightly from the 22nd day of cultivation and did so at further lower densities. Almost all NAR values lie over the control value at the last measurement. The chlorophyll content in mg g^-1 dry matter of the overground parts rose with stand density to density "40" (41% more than at density "5"); afterwards it dropped. The accumulation (in mg g^-1 d.m.) of phosphorus ions was higher in the plants from dense cultures compared with density "5", particularly in the roots. The accumulation of potassium was near to the control value ("5"), while that of nitrogen was lower. The utilization quotients of phosphorus and potassium in denser stands were the same or negligibly lower than at density "5". They were a little higher in nitrogen than in the controls. Also the ratio RGR/I_M was a little higher than in denser stands. The root-weight ratio, the accumulation of elements in mg g^-1 d.m., the chlorophyll content in mg g^-1 d.m., NAR_ch, the utilization quotient, and the ratio RGR/I_M differed qualitatively by the densification of the culture (with complete mineral nutrition) from the influence of element deficiency (at the same stand density).

Bei 14 Winterweizensorten wurde im Zeitabschnitt Winter-Frühling der Zellsaftbrechungsindex gemessen. Die höchsten Werte wurden bei einigen frostresistenten, die niedrigsten Werte bei nichtresistenten Sorten gefunden, der Zellsaftbrechungsindex war aber nicht in allen Fällen der Frostresistenz proportional. Mit Rücksicht auf Stoffwechselvorgänge der osmotisch aktiven Stoffe, die deren Menge und Verhältnis bestimmen, sind Saisson- sowie Tagesveränderungen im Laufe von Winter und Frühling nicht nur von der Temperatur und Feuchtigkeit der Umgebung abhängig. Der Zellsaftbrechungsindex unterliegt verschiedenen Veränderungen in Beziehung zu Pflanzenernährung in verschiedenen Wachstumsphasen bei Sorten mit verschiedenem biologischen Charakter und unter verschiedenen pedologischen und klimatischen Bedindungen. Stickstoffdüngung erhöht den Zellsaftbrechungsindex bei vielen Sorten, hauptsächlich gm Winter.

From the very continental high mountain basin Dasht-i-Nawor in Central Afghanistan an example of the daily course of some important ecological factors is given (irradiance, air, leaf and soil temperatures, water vapour saturation pressure deficit, evaporation rate, wind velocity) and some ecological characteristics (osmotic potential, refractive index and chloride content of the cell sap) of two species one of them being a facultative halophyte

An investigation was carried out on ability of Ypenyl,i.e. 5-bis-(2-chloroethyl)-aminomethyluracil to induce structural disturbances of chromosomes and changes of mitotic activity of meristematic cells ofVicia faba. The cytostatic employed induced chromosomal aberrations mostly of the chromatide type, the greater part of which were localized in the group of small chromosomes. The frequency of aberrations was proportional to the concentration of the substance used as well as to the duration of treatment. After a 24 hour treatment with 0.01mm solution of Ypenyl the maximum incidence of aberrations was found after 8 hour recovery in water. Longer recovery periods resulted in a gradual decrease in the number of aberrant post-metaphases in the cell population studied. Increasing concentration of Ypenyl led to the decrease in mitotic activity. Short recovery periods caused a considerable decrease in the mitotic index, which was compensated as late as 16 hours after treatment with the cytostatic.

Genotypic, phenotypic and environmental correlations were ascertained in a set of 18 winter wheat varieties from experiments conducted for two years on two levels of mineral nutrients. Analysis of genotypic relationships found between yield components, area and length of the last leaf, angle of the second leaf and length of the plant at heading time was made using Wright's path coefficients.
In some instances the analysis showed, in comparison with simple genotypic correlation in reality, a different direct association of the pair of characters, the causal basis of which consisted in a relatively high indirect effect of other variables used in the experimental model.
From results cited it may be judged that the effect of the last leaf area was at least under our experimental conditions closely associated with both factors of ear productivity,i.e. with number of grains and average weight of one grain. The influence of the angle of the second leaf (next to the last at the top) was associated first with the number of productive stems, thus rather with a factor of productivity of plant stand and only in a wider action with the average weight of one grain.
In the future it will be useful to confirm the effect of subcharacters as additional criteria in the selection of plant types with higher prospective yield. From preliminary, as yet unpublished results, the use of selection indices in winter wheat may be considered an available method for estimating the expected genetic advance from the selections.

Comparative cryoscopic determinations of osmotic pressure and the refractive index of cell sap were analyzed with the aid of correlation coefficients and characteristics of the trend of their course (by means of the slope of the regression lines and probability field). It was confirmed that an indirect estimation of the osmotic pressure of the cell sap is readily feasible refractometrically and that it is sufficiently reliable if a relationship between the two values is determined experimentally in advance. The biological homogeneity of the material tested influences this relationship, both genetic and ontogenetic. This conclusion followed from the evaluation of the correlation between osmotic pressure of cell sap and its refractive index in leaves ofHordeum sativum Jessen. The significance of biological homogeneity was brought out by the classification of all measured pairs of values into groups according to varieties and according to leaf insertion.

The effect of sowing density (21, 85, 340 and 3400 plants per 1 m on the leaf area index (LAI), vertical arrangement of developing foliage and dry matter production was investigated in stands of wheat (Triticum aestivum L. cv. Niva).
1. With increasing sowing density.
a) The LAI increased and the highest LAI = 9.6 was obtained with 3400 plants. m-2. The largest development of foliage took place at ear emergence with 85, 340 and 3400 plants. rn-2, and in the flowering phase with 21 plants. m-2.
b) The overal leaf area duration was reduced, with a difference of 11 days between the lowest and the highest density.
c) The number of leaves formed per one stem increased from 5 to 8.
2. An increase in theLAI affected the vertical distribution of leaf area and resulted in increased differenoes in relative light intensity between the top and bottom layers of the leaf canopy. Differences inLAI were linked with differences in leaf area duration and in the relative proportions of leaves of different age in the total number of leaves per 1₂
3. a) Shoot dry matter production increased with increasing density; the maximum of 3811 g. m_-2 was obtained with 3400 plants._M-2.
b) The dependence of grain yield on sowing density had a parabolic character; the maximum yields of 47001 g. m-2 and 442.8 g m-2 were obtained with 340 and 85 plants. respectively.
c) The optimum LAI for the formation of grain yield was 2.3 to 3.2.
d) The crop growth rate (C) increased with increasing density; the highest mean recorded C = 594 g. m. week-1 corresponded to LAI = 9.6.
4. Thinning the stands of 3400, 340 and 85 plants. m-2 in the phases of the 3rd leaf (22 days after sowing) and of tillering (30 days after sowing) to the next lower density resulted in a reduced LA leaf and tiller number, crop growth rate, shoot dry matter production and grain yield as compared with both the initial and standard densities. The role of foliage with respect to both maximum dry mater production and maximum grain yield was defined by an optimum range of relations between the rate of foliage development, leaf area, vertical structure and distribution of light intensity within the stand operating as a self-controlling system.

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.

Mosaic disease ofAnchusa officinalis found at a ruderal association in Prague-Holešovice in the close proximity of TMV infected cruciferous weedsCardaria draba andSisymbrium loeselii, was identified to be caused by the same agent-the necrotic TMV-strain.

A study was made of the effect of substituting a short day for vernalization as a varietal characteristic of winter wheat. Varieties representing certain ecotypes were vernalized for different lengths of time and it was studied how a short day can replace or accelerate vernalization. At the same time data were obtained on the effect of a short day on individual criteria of growth. The results showed that there are ecotypes in which a short day does not replace vernalization (the varieties San Pastora and other Italian varietis). In this case growth inhibition did not occur either. Otherwise it usually accompanies the substituting affect of a short day. This finding permits the interpretation of varietal differences observed in association with short day growth inhibition and changes in carbohydrate metabolism conditioned by it. Growth inhibition produced by a short day is a general reaction which is not only associated with vernalization. The author found varieties (Chlumecká 12) in which growth was inhibited by short day without accelerated development occuring (alternative types).

Parallel measurements of the osmotic pressure (cryoscopic method) and the refractive index of cell sap were carried out on 246 samples from seven plant species. At the same time both values were ascertained as well as their relation for aqueous solutions of some sugars, organic acids and inorganic salts. The relations found with these model solutions are different for different substances. The quantitative composition of osmotically active components of cell sap changes in the course of ontogenesis and as a result the relation of refractive index and osmotic pressure also changes. By this comparison it has been shown that a reliable and more or less linear relation of the two values, which is advantageous for practical application, is only valid for a limited period in the ontogenesis of the experimental plant. The determination of the osmotic pressure of cell sap from the refractive index, the main advantage of which is its quickness and the small volume of sap required (0-02 ml.), is reliable if we construct empiricallyad hoc the appropriate correlation graph for the experimental plant for a limited ontogenetic period.

A study was made of the influence of N-formylbiuret, a degradation product of 5-azauracil, on the course of mitosis in the meristem of the roots ofAllium cepa. In the presence of N-formylbiuret in a concentration of 4-10^-3 M in the nutrient fluid there is a decrease of 20 to 30% in the mitotic index of the meristem of the roots. This decrease in the mitotic index can be prevented by the addition of ureidosuccinic acid or uracil to the medium. N-formylbiuret which, as a result of interaction with dihydroorotase, inhibits the biosynthesis of the pyrimidine precursors of nucleic acids, does not display irreversible toxicity when observing its cytological effect. When decreasing the mitotic index with N-formylbiuret no chromosomal aberrations were observed in the anaphase or telophase.
Under the same conditions, the structurally similar halogenacetyl derivatives of urea in decimally smaller concentrations show marked cytotoxicity with the agglutination of chromosomes. The reversion of the antimitotic effect of these substances by the pyrimidine precursors of nucleic acids was not demonstrated.

Biological tests of waters combined with determinations of their chemical nature make it possible to classify different types of waters, but usually one figure does not suffice for a correct evaluation of a given water.Gabriel's biological index is a valuable criterion which can give us a good deal of information about the state of the water if the necessary conditions are adhered to; it is not, however, a completely quantitative method and value.
The total body of producers, that is photosynthetizing matter (autotrophs) compared with the total organic matter as a whole [the body of consumers plus reducers (destroyers) plus dissolved organic matter] would be a much better criterion for characterizing the waters than a simple count of various individual bodies, even if this were to be supplemented by the relevant indices.
The usual conventional method, employed hitherto, of a biological oxygen demand must be supplemented by a similarly standardized conventional method of biological production of oxygen.
The literature on the subject gives many different methods for establishing "organic carbon" and chlorophyll; the most important of these have been evaluated critically and experimentally byŠestÁk (1955, 1958a, 1958b). Of a number of tested modifications the procedures outlined in this article proved to be the best. The relationship between producers and consumers plus destroyers must always be simplified. We cannot content ourselves with a figure or an equation, but must respect other factors as far as possible.

As the species hybridSalvia němecii (= S. nutans x S. jurišićii) is highly fertile, genetic analysis of the segregating F2 generation has been carried out. In 238 plants of F2 the following leaf characters were investigated: type of the vascular bundle course in the petiole, the ratio of the petiole to leaf blade length, the ratio of the length of the leaf blade to the breadth, and the segmentation of the leaves, i.e. ratio between an ideal contour surface and the actual surface of the leaf blade. All these characteristics were compared with those of the original parental species as well as of the F1 generation. It was found that:
1. Type II of vascular bundle course has simple dominance over type III (segregating ratiol72 : 66, X²(1) = 0.94, P = 0.35).
2. All morphological characteristics of the leaves behave as though governed by polygenic systems. The segregation in F₂ is always very wide and the extreme segregants exceed the values present in both parental species.
3. The type of vascular bundle course in the petiole is inherited independently of the morphological signs of the leaves. There is practically no correlation between vascular bundle type and any of the morphological ratio indices.
4. Between the morphological characters, on the other hand, there are significant correlations, especially between the length of the petiole and segmentation of the leaf (r = 0.31), and between the segmentation and the length-breadth ratio (r = -0.42). Therefore, some of the polygenes concerned may be linked together, i.e. localized in the same chromosome, but most of them are transferred independently.

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 spraying of 26-day-old sunflower plants with a solution containing 50 μg. gibberellic acid/ml. brought about morphological changes in leaves and a statistically significant increase in the leaf shape index (length: width of leaves). The number of leaves on the stem also increased, together with a rise in the value of the ratio of dry weight of stems to dry weight of leaves.

Within one leaf blade there are considerable differences in hydration of its parts. Marked longitudinal, transverse and area gradients of the osmotic pressure of cell sap were ascertained within the leaf blade of sugar beet. The osmotic pressure was determined indirectly by the refractive index according to the empirically established correlation refractive index: osmotic pressure (measured cryoscopically) cf. fig. 1. The gradient from the base of the blade to the tip ranged around plus 40% of the osmotic pressure at the base. This and other gradients mentioned were not noticably changed even when the leaves were artificially saturated with water or when water deficit arose or was adjusted by actual changes in the water balance. (In all these experiments the polarity of the transpiration stream was maintained.) The stability found in various degrees of hydration of individual parts of the adult leaf blade indicates that the variability is a result of the previous ontogenetical development of the leaf as a polar organ and of the fact that the adult leaf remains essentially unchanged by the actual changes in the water exchange. The heterogeneity found in the leaf with regard to the values here dealt with is an expression of the physiological heterogeneity of the leaf blade. ation intensity is concerned, it has been theoretically established that only after the reduction of turgor to nought does increased osmotic pressure of cell sap start to act as a factor in reducing transpiration, and that this reduction is under normal conditions comparatively small (Renner 1915, Stalfelt 1956).