When examining plants of white mustard (Sinapis alba L.), a significant relationship between the size of the roots and the yield was found, both in a pot experiment and in a field one. The yield was influenced by the size of the root system during and after flowering time. Especially the number of seeds has increased, and the average weight of seeds showed the same tendencies after the flowering time. The productivity of plants with an above-average yield was increasing more quickly than the size of their root system. From the beginning of the vegetation till the end of flowering these most efficient plants showed the lowest permitivity dispersion and the highest dispersion after the flowering time. The dispersion has increased towards the end of vegetation.

Pea plants grown in nutrient solution in which K⁺ ions were equimolarly replaced with Na⁺, NH₄⁺ or Rb⁺ did not show morphological symptoms of potassium-deficiency. The activity of diamine oxidase in these plants was higher than in controls. Similarly higher diamine oxidase activity was found in plants grown in a complete nutrient solution supplemented with putrescine.

In Vietnam a green strain of tobacco mosaic virus was isolated having TIP 89°C (10 min) and causing systemic necrosis in tobacoo 'Xanthi-nc' and sometimes also inDatura stramonium. In symptomless tomato plants an elongated virus belonging apparently to the Carlavirus group (NL 630 nm) was found. In papaya trees showing severe symptoms of mosaic and/or ringspot elongated virus particles (NL 730 nm) were observed; this virus being apparently a member of the Potyvirus group, resembled as far as its symptoms in papaya are concerned, the papaya ringspot or the distortion ringspot. In Cambodia some young rubber trees showed malformed leaves (esp. edges and veins) with yellow discolorations along the veins. Such leaves contained elongated virus-like particles (rigid or slightly flexible) of various length (60 to 880 nm), so that their normal length (NL) could not be established precisely. Particles 120 to 150 nm long occurred very frequently.

Physiological effects of volatile substances released by the overground as well as by the underground organs of higher plants were studied. The activity of the volatile substances was tested both when these substances were allowed to act directly in the air and when they were dissolved in water in the form of solutions. Plants which do not contain essential oils or which are not rich in them as well as those abounding in essential oils and other volatiles were used in the experiments. The physiological activity of the volatile substances was tested on rye seedlings.
The overground as well as underground mature organs of the tested plants were found to release volatile substances causing, when acting directly, in the majority of cases an inhibition of the growth in length and of the formation of dry matter in rye seedlings. A pronounced inhibition of the growth of rye seedlings was brought about especially by the volatile substances of "aromatic" plants such as common dill, wild thyme, yarrow milfoil, garden thyme, marjoram, etc. The volatile substances released by the organs of "non-aromatic" plants like sugar-beet, common sunflower, quackgrass, etc., were found to bring about a significant inhibition of the growth of rye seedlings, too.
The volatile substances released by the plant organs were found to be altogether absorbable in water and physiologically active also in the form of water solutions. With the exception of volatile substances from hemp and quackgrass leaves, which brought about a mild stimulation of the dry matter formation in rye seedlings, inhibitory effects of these solutions were found to prevail in all cases. Most effective were the solutions of the volatiles from some of the "aromatic plants".
An assay for olefines in the atmosphere of the experimental vessels demonstrated that in almost all cases ethylene is being released by the plant organs.

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

Treatment of two-week-oldBrassica campestris andTrigonella foenum-graecum plants with morphactin andVicia faba, Antirrhinum orontium, andPapaver somniferum with Niagara, induced marked variations in the orientation and ontogeny of stomata and the epiderma cells. Morphactin-chlorflurenol at 12.5, 62.5, 125, 250, and 500 ppm, caused marked damage of the shoot apices and changes in the epidermal tissue, such as divisions of the guard cells, reduction in the size of the stomata, and epidermal cells. Niagara-ethyl-hydrogen-1-propylphosphonate at 100, 500, 1 000 5 000, and 10 000 ppm caused thickenings of the epidermal cell walls and differentiation of new meristemoids from the epidermal cells, contiguous stomata, and incomplete development of the guard cells.

The investigation of the hormonal nature of plant flowering in connection with their photoperiodic reaction has shown that flowering depends on a bicomponental system of hormones, gibberellins regulating stem formation and growth and substances of the anthesin type regulating flower formation. In agreement with the division of the photoperiodic reaction into a leaf and a stem phase the study of the internal factors acting on plant flowering was carried out by means of leaf and stem (apex, bud and callus) models. The results obtained from work with leaf models proved the presence of two groups of hormones of flowering in plants. The data obtained from the application of stem models pointed to the localization of the action of gibberellin and anthesin in different zones of the shoot apices and characterized the potential capacity for flower formation of isolated callus tissue of neutral and photoperiodically sensitive species.

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 effect of phosphorus deficiency on anthocyanin content in tomato plants was studied from the point of view of pathological anthocyanin formation. Phosphorus deficiency resulted in an evident increase of anthocyanin content in all experiments, independently of the tomato variety and of the cultivation conditions. The anthocyanin amount was five times higher on the average and the differences were statistically significant. The average growth inhibition of tomato plants under phosphorus deficiency was 18%. Accumulation of anthocyanins is limited by the temperature; anthocyanins are not synthesized at temperatures above 30°. The results of the experimental variant with enhanced phosphorus concentration in nutrient solution were not uniform. In some experiments a decrease of anthocyanins accompanied by slight growth stimulation was observed, in others an increase associated with growth inhibition. It seems that cultivation conditions, especially the light intensity, play an important role in these experimental variants.

We studied the significance of actual accessibility of ions for presence of α-amylase in roots and cotyledons of young pumpkin plants. We considered α-amylases to be-in agreement with published data-amylolytic enzymes which lose their activity after being dialysed against EDTA or a dilute solution of hydrochloric acid and which can be reactivated by addition of Ca²⁺. N connection with activity and Ca²⁺ nutrition appeared in cotyledons; it did, however, in roots: Ca-deficient plants revealed after preparation either completely inactive enzymes or enzymes with slight activity. It was, however, possible to reactivate them by addition of Ca²⁺ during preparation.
So, using polyacrylamide disc electrophoresis we present evidence for the appearence of amylase with typical characteristics for α-amylases of other sources. Its relative mobility was the same for isolates from both roots and cotyledons. Its biosynthesis was not dependent upon metal which is associated with enzyme. No conclusion can be drawn as to whether Ca-deficient α-amylases are activein vivo; therefore it was impossible to judge whether α-amylase activity is subject to feed-back regulation.

The effects of soaking seed in 2-chloroethylphosphonic acid (CEPA) for 24 or for 48 h on the cumulative 5-day seedling growth ofCucumis sativus L. (cucumber) andPisum sativum L. (peas) were studied. Each cucumber seed absorbed an average of 0.015 ml of CEPA solution, while pea seed absorbed 0.365 ml, over a 24 h period.
In cucumber, 240 mg l^-1 CEPA concentration decreased radicle length by 23%, regardless of soaking duration. The same concentration increased radicle weight in a 24 h soaking duration, but decreased radicle weight when soaking was for 48 h. At 48 h, CEPA concentrations of 0.24 and 2.4 mg l^-1 increased plumule growth by 26%. In peas, the 240 mg l^-1 decreased the length and the weight of both the radicle and the plumule in a 48 h soaking duration, but had no significant effect at a 24 h soaking. At the low concentration of 0.24 mg l^-1, seedling growth was stimulated by over 30%.
Cucumber was 3 times more efficient than peas in the utilization of CEPA for seedling growth, in terms of total fresh weight of seedling per microgram of CEPA absorbed: 1 127 and 274 mg μg^-1 CEPA in cucumber and peas respectively. Extrapolative calculation, using cucumber responses as standard, suggests from this seedling study that about 12 mg l^-1 CEPA is likely to stimulate growth and/or yield in sprayed pea plants.

During our studies on the interaction of anthocyanins and plant virus diseases, reproduction of sugar beet mosaic (SBMV) and tobacco mosaic viruses (TMV) was investigated. Experiments were carried out in leaves of sugar beet,Beta vulgaris cv. Dobrovicka N and its spontaneous anthocyanized mutant. SBMV induces a systemic infection while TMV is responsible for primary local symptoms in sugar beet leaves only. Our quantitative analyses onAmaranthus caudatus L. andChenopodium quinoaWilid. showed a significant decrease in concentration of SBMV in juice extracted from anthocyanized beet plants as compared with extracts from normal green infected plants. Significant differences were also obtained when SBMV - containing juice was tested in mixtures with healthy extracts from anthocyanized and normal green plants. Also the intensity of TMV symptoms in beet leaves was considerably decreased in leaves of antho-eyanized plants.

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.

The methyl-ester of 2-chloro-9-hydroxyfluorenole-9-carboxylic acid (Chlorflurenol-Methyl =CFM) enhances the elongation of intact plants ofColeus blumei and induces leaf curvatures and an anormalous abscission of the youngest leaves. In long-time-experiments (3-4 month), CFM induces increased outgrowth of the axillary buds including leaf deformations and abscission of organs on the originating shoots. CFM stimulates the adventitious root formation of cuttings fromHelianthus, Phaseolus, andColeus. It is shown inColeus cuttings that an inhibition of root formation precedes the stimulation of root formation. Gibberellic acid does not influence any one of CFM-induced effects. Therefore morphactins are not GA₃-antagonists. TIBA qualitatively causes the same effects as CFM. Therefore it is possible that the mechanisms of actions of both substances are similar.

Metabolic changes in tomato plants infected with potato leafroll virus were followed. The virus was transferred by grafts taken from diseased tomato plants. Sharp changes in the respiration rate and in the activities of the investigated enzymes observed before the concrescence of the graft with the stock are obviously connected with the defence reactions of the plant. In the roots of the experimental plants a nearly complete correspondence of the course ofo-diphenol oxidase and ascorbic acid oxidase activities with the respiration rate occurs. In the shoots the respiratory chain with ascorbic acid oxidase as terminal oxidase is involved, whereas both chains probably take part in the respiration in the roots by which a link with sugar degradation is achieved. The rate of glycolysis and that of pentose phosphate cycle in the roots of experimental plants are nearly identical. The comparison of glucose-6-phosphate dehydrogenase activity with ascorbic acid oxidase activity reveals that both curves show the same course, which indicates the presence and action of a respiratory thain with ascorbic acid oxidase functioning as terminal oxidase.

In comparison with controls, the respiratory activity in locally infected leaves was lower until the 8th day after inoculation, whereas it was higher with the leaves in which systemic infection was expected. In the course of the remaining period of investigation, the respiratory activity was almost identical in both cases, showing a rising tendency. Ascorbic acid oxidase whose activity curves correspond to those of respiration, represents the main terminal oxidase. Its activity is probably coupled to the respiratory chain in which glutathione, reduced by NADPH, is capable of reducing reversely dehydroascorbic acid originating from the action of ascorbic acid oxidase. Virus Y-infected plants containing excess NADPH, as found out in our previous paper, the respiratory chain mentioned is likely to be utilized preferentially.

Changes in the metabolic pathway linked up directly with respiratory pathways were followed inN. tabacum L. cv. 'Samsun' plants inoculated with potato Y virus. The consumption of oxygen in infected tissues before the occurrence of visible symptoms (up to the sixth day) was lower than in control plants, then it started to rise and the tenth day after inoculation it reached 116% of the control. It was established that two main respiratory chains were involved, from which the glutathion-ascorbate system was responsible for the total respiration rate during the entire period of investigation.
The other respiratory system,i.e. NADPH-glyoxalate-glycolate, is not related directly to the respiration rate, but, it is probably linked up with the changing content of NADPH. The results obtained with catalase and peroxidase show that these enzymes are not directly linked up with changing glycollate oxidase activity but that they cooperate. While at the beginning their activities are mutually compensated, at the later period of enhanced glycollate oxidase activity and increase in the activities of both these enzymes occurs which then remove the originating excessive toxic H₂O₂.

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.

A non-specific effect of antiviral factor (AVF) was proved by interference of five different viruses (CMV, PVX, PVY, TMVe, TMV vulgare) with CBRV.
The non-specific AVF originates in non-infected tissues around TMV lesions. Transmitted mechanically to other plants this AVF exhibits the same suppressive effect on multiplication of TMV and CBRV.
The AVF is formed in the non-infected apical part of the leaf which was infected in its basal region. The susceptibility of leaves is decreased even when AVF is added to virus inoculum and applied mechanically on the leaf. The apical part of the leaf the base of which is met with necrotic reaction to TMV, is considerably less susceptible and TMV multiplication in this region is decreased. The necrosis on the leaf base induced by mechanical injury or by cysteine hydrochloride may decrease the susceptibility of the leaf to some extent, but has no effect on multiplication of the virus.
The activity of AVF in healthy apical region of the leaf increases till the fifth to the eighth day after its basal part was infected. The apical region then exhibits lower susceptibility (decrease in number of lesions) and the growth of lesions is decreased. This indicates the virus multiplication being suppressed.

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 mutual relationship between the water potential (γ _w ), its components, namely the osmotic potential (γ _s ) and the pressure potential (γ _p ), and the water saturation deficit (ΔW _sat ) were determined in the leaves of different insertion levels. During the water stress development in kale plants induced by decreasing soil moisture theγ _w decreased, parallely in all the leaves but the same decrease ofγ _q was accompanied by the highest decrease of theγ _p , probably due to the accumulation of osmotically active solutes, and the lowest decrease ofγ _p in the upper leaves and with the lowest decrease ofγ _s and the highest decrease ofγ _p in the lower leaves. Also the corresponding values of the ΔW _sat were always lower in the upper than in the middle and lower leaves. Thus the upper leaves wilted at more negative values ofγ _w than the other leaves. On the contrary, during the wilting of the cut off leaves the relationship betweenγ _w and ΔW _sat in the upper, middle and lower leaves was practically the same. The very slightly higher decrease ofγ _s in the upper leaves in comparison with the other leaves was compensated by a lower deerease of theirγ _p .
These changes in the ratios ofγ _w ,γ _s ,γ _p and ΔW _sat with the leaf insertion levels enabled the preference of the upper leaves in retaining the necessary water supply during the wilting of plantsin situ.

In dialyzed extracts from winter wheat plants an intensive enzymatical transamination reaction occurred between L-α-alanine and α-ketoglutaric acid (L-α-alanine + + 2-oxoglutarate = pyruvate + L-glutamate, EC 2.6.1.2) as well as a weak nonenzymatical transamination reaction, practically immeasurable. Pyridoxal-5'-phosphate strongly affected the reaction rate. Besides the transamination product-glutamate, γ-aminobutyric acid was formed in this reaction. This amino acid could have originated neither via proteolysis of the enzyme extract, nor via decarboxylation from glutamate formed, nor via transamination of succinic-γ-semialdehyde after α-ketoglutarate decarboxylation. This was the only case of its formation in the transamination reactions investigated in our laboratory - it originated from the alanine-glutamate reaction only, and the mechanism of its biosynthesis cannot be elucidated for the present.
Dialysates from shoots exhibited a significantly higher enzymatic activity in comparison with those from roots.
The effect of trophic conditions (Knop's nutrient solution, a water solution of potassium humate, water) was not revealed when calculating per dry weight unit. However, when calculating per protein unit an increased activity was found in the dialysates from shoots of both nutrient - deficient variants. Roots of plants cultivated in potassium humate had the lowest activity.
The discussion concerns the possibility of an adaptive use of this transamination for increasing the essential glutamate level in green parts of the plants cultivated under unfavourable nutritive conditions, and also deals with a further characteristic of the differing metabolism of plants cultivated in humate.

The content of substances showing the cytokinin activity was estimated on decapitated and one-cotyledon-deprived pea plants during that period when the promoting effect of the cotyledon excision had not yet been manifested. Results of the bioassay showed that after the excision an increase in the level of substances with cytokinin activity occurred only in cotylars growing in axillas of these excised cotyledons. These results coincide with earlier data about the content of gibberellins and auxins in the same object.

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.

The dynamics of the uptake by barley plants of trimer phosphonitrile-amide [PN(NH₂)₂]₃ labelled with³²P was studied. It was shown experimentally that the covalent compound [PN(NH₂)₂]₃ enters the plants more rapidly than (NH₄)₂HPO₄. Hence it was concluded that the mechanisms of the transport of [PN(NH₂)₂]₃ and (NH₄)₂HPO₄ into the cells, across the cell membranes, are different.

Ethylene was collected in methanol solution of mercuric acetate and the addition compound formed was then separated by means of paper chromatography. The spot area and colour intensity after detection were determined using a densitometer. The amount of collected ethylene was calculated from a calibration curve.
The ethylene liberated from plant samples was collected during one or two days. During this period the amputation of the whole plant organs did not influence ethylene production. Changes in ethylene production were found after segmentation of the tissue or after the treatment with auxin and Co²⁺ ions.
The above-ground parts of investigated herbs released 0.3 to 3.5 μl of ethylene per kg fresh weight per hour. The leaves of investigated trees released 1 to 20 μl of ethylene per kg f.w. per hour. The rate of the production of ethylene seems to be specific for a given species.

The development of temporary water stress during the day-light hours, characterized by a decrease of the values of the water potential (ϕ_w) and increase of the values of water saturation deficit (ΔW_sat) was found not only in the leaves of intact kale plants but also in cut leaves with their petioles immersed in water. These results indicate that the leaf resistance to water transport could not be supposed as negligible. The same decrease of ϕ _w was accompanied with the higher increase of ΔW_sat in cut leaves than in leavesin situ.

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.

In dialyzed extracts from winter wheat plants transamination reactions occurred between asparagine and α-ketoglutaric acid (L-asparagine+2-oxoacid=2-oxosuccinamate+ +amino acid; 2. 6. 1. 14). Reactions with pyruvate exhibited a very low activity. Besides transamination products,i. e. glutamate and alanine, aspartic acid was formed in both reactions. Deamidation was more intensive in the weak reaction asparagine-alanine and less intensive in the asparagine-glutamate reaction.
When calculated per dry weight unit the activity was the same in plants of all variants (three experimental variants-Knop, potassium humate, water). A higher, activity was found in root dialysates; however, a highly significant difference could be observed only between shoots and roots of Knop variant. When evaluating results in terms of protein content we found a significant difference between mineral variant (Knop-the lowest activity) and both deficient variants (potassium humate, water-the highest activity). Thus the highest growth activity was in connection with the lowest transamination activity and vice versa, which was the same as in transaminations of aspartic acid. In the case of asparagine, too, one can consider the possibility of its utilization via transamination for biosynthesis of glutamic acid in plants which have, for reasons of nutrition, a low level of this metabolically important amino acid.

A simple modification of a laboratory gravimetric technique for the study of transpiration of intact plants is described, by which the process can be followed continually. The plants are grown in light vessels on a light "keramzite" or other suitable medium, either alone or in combination with agar gel. The mineral component provides for the necessary cultivation properties of the medium, whereas agar gel ensures steady and undisturbed water relations in longer experiments.
The calculation of the transpiration intensity per unite of time is described. For reliable results the number of samples must be lange chough, so that the coefficient of variation does exceed 10 per cent. The determination of the transpiration is sufficiently exact even without a correction for changes in dry solids, the absolute increments in dry solids during the time interval studied being of a smaller order of magnitude than the values of transpiration. The results are expressed per fresh weight of the transpiring unite, by which an undisturbed transpiration study of a longer duration is rendered possible and the effects on the plant are excluded.