On Changes of Osmotic Concentration in Certain Plants By I. Qhga The osmotic concentration of the cell sap in various plants of different habitats, such as water plants, desert plants and marsh plants, has been found to show great variation by the works of DRABBLE and DRABBLE~2~, CAVARA~l~, FITTING~4~, HARRIS, LAWRENCE and GORTNER~s~, and ILJIN, NAZAROVA and OSTROVSKAJA~8~. These authors further state that if the same species of plants are subjected to the different habitats, the osmotic concentration varies : that is, if a given plant is growing in dry land, on rock or in salt marsh, the osmotic concentration is usually high, whereas plants of the same species found in water, gardens or woods have, as a whole, low osmotic concentrations. HARRIS, GORTNER, and LAWRENCE~5~, EWART~3~ and ILJIN~7~ UR- SPRUNG and found that the osmotic concentration in the cell sap of leaves of a given plant depends upon the height of the insertion of the leaves ; also in the guard cells of stomata the osmotic concentration varies during the day and night causing the changes in stomatal opening. Thus it is quite evident that the osmotic concentration of the cell sap differs in different species, in the same species in different habitats, and also in the same plant under the influence of environmental conditions and of its own life processes. STANGE~9~ cultivated plants in KNOP's solutions, using a range of concentrations, and was able to increase the osmotic concentration of the cell sap. The writer has made some comparative observations with reference to the variations in osmotic concentration of cell sap of certain plants associated with growth in dry soil, in concentrated solutions and under normal conditions. This report is the result of experiments mentioned above.
588 THE BOTANICAL MAGAZINE [vol. XL. No. 4;s METHODS AND MATERIALS The method of plasmolysis has been used throughout, the plasmolysing agent employed being sucrose. Solutions differing by a unit in the second place of decimals were made up from 0.20 to o.8o gram-molecular strength. Whenever it was found useful to use i or 2 molecular solutions they were added to the above series. To observe the effects of the solution on leaves, the epidermis, stripped from the surface of the leaf, was immersed into the solution ; sometimes mesophyll tissue was observed. Root cells and root hairs were also observed. Usually separate portions of tissue were placed in each solution of the series but sometimes the same tissue was transferred from the low percentage solution to the higher. The values given for osmotic pressure are those of the solutions in which plasmolysis first begins. This point was clearly detected after some experience of the method. The time allowed was i o minutes. The penetration of solution took place more readily into mesophyll cells than into the epidermis of leaf. The plants used in these experiments were wheat, buckwheat, broad bean and coleus. EEXPERIMENTS AND RESULTS (1) Seedlings were started in moist chambers which were prepared by placing a moist blotting paper on the bottom of PETRI dishes. When the length of roots reached about 5 to 8 cm., the osmotic pressure of the root hairs was measured. The results were as follows : Broad bean.22-.24 M. sucrose. Wheat.24-.26 M. Buckwheat.22-.24 M.. (2) The osmotic pressures during a later stage of growth (about 14 days later) in water- culture and in pot culture were as follows : Height of Water culture Pot culture Plant leaves roothairs leaves roothairs Broad bean 30 cros..32-.50.36-40 44 36 Wheat 15 cms..46-.48.46-.48.36-.38.36-- 38 Buckwheat. 20 cms..52-.54 40-.50 40-42.3o- 40 Coleus. 15 cms..30.30 (2a) The osmotic pressures of leaves of plants of the same age in
Nov., 1s261 L OIIGA-OSMOTIC CONCENTRATION 589 pot culture without any added water for the last four days of their growth. Broad bean.38-.6o Wheat.46-.62 Buckwheat.52-.6o Coleus.36-.38 The plants had reached a stage of permanent wilting. (3) Plants of the species above mentioned either sown or grafted in 4 inch flower pots, 10 pots to each species. Each set of 1 o pots was divided into two groups, 5 pots in each. One group was well irrigated and the other group kept dry. When the plants in the second group wilted they were brought back by watering. This process was repeated four or five times during the period of two weeks. The both groups were watered equally and immersed into i M. sucrose solution, pot and all, in order to ascertain wilting time. In every case, the wilting was reached earlier by the plants in the moistened pots than by those in the pots subjected to intermittent drought. The osmotic pressures of leaves of these plants were as follows : Regular watering In termitient drought Broad bean.32-.36.38-.40 Wheat.36-.38.38-.46 Buckwheat.40.30 Coleus.30.38 (4) Cultures in sugar solution. Seedlings of wheat and of buckwheat which had developed to 10-12 cm. length in water cultue were placed in a range of sugar solutions in tumblers of 300 c.c. capacity. Experiment a Wheat seedlings placed in sucrose solutions of.24 M. concentration and above, wilted in one hour in the room. However, they were recovered in tap water after about 20 hours and again placed in sucrose solution of the same strength (.24 M). Then wilting did not take place until about 20 hours later. They were again treated in tap water and after recovery placed in the same molecular sucrose solution. This was repeated three times. Finally, five days later, these cultures turned yellow without wilting. This experiment was
590 THE BOTANICAL MAGAZINE [Vol. XL,. No. 479 repeated. This time wilting took place in 2 hours in solutions of 24 M solution and above. The subsequent treatment was as before and again the plants without wilting turned yellow after the period of five days. Experiment b Buckwheat In the case of buckwheat, plants placed in.26 and above molecular solution wilted 4 or 5 hours after. But next day without addition of tap water they recovered and were apparently healthy. Subsequently they gradually wilted and finally died after 30 days. The osmotic pressures of leaves of these plants taken 5 days after the first sucrose treatment was found to be.8o-i.o M. sucrose. An interesting phenomenon observed in the buckwheat grown in sucrose solution of. i o-.6o M. was that in those cultures aerial roots began to grow from the stem. CONCLUSION The above results indicate that the cell sap of plants has a different osmotic concentration in the young stages, older stage, and in a wilted condition, and frequently the cell sap of the stem and roots of the same plant have different concentrations. So far as the experiments went the maximum increase in osmotic pressure produced by restricting water supply to the roots as by immersion in sucrose solutions was up to.8-i.o M. sucrose. Among the plants grown in high sucrose concentration some continued to live in.8o- I.o molecular solution of cane sugar. But they developed very slowly indeed. In this case it seems clear that the external force which would be required to induce permanent wilting would be more than 18.7 atmospheres (.8 M. sucrose). SUMMARY (1) The osmotic pressure of leaves and roothairs of plants varies in different stages of growth. (2) Restriction of water supply causes an increase in this osmotic concentration. (3) Wheat and buckwheat seedlings placed in sugar solution
Nub'., ] 926] I. OHGA-OSMO TIC CONCENTRATION 591 of higher the leaves molecular concentration than that required to wilted at first but recovered and continued to plasmolyse live. Educational Institute, Dairen, Manchuria July, 1926 LITERATURE CITED I 2 3 4 5 6 7 8 9 IO II 12 I3 CAVARA, F., Resulti di una serie di sicherche criseopiche sui vgetali. Contrib. alla. biol. veg. 4: I-, 1905 DRABBLE, E. and H. DRABBLE, The relation between the osmotic strength of cell sap in plants and their physical environment. Biochem. Journ. 2 : II7- I32, 1907 EWART, A. J., The ascent of water in tree. Phil. Trans. Roy. Soc., London, B, 198: 41-86, 1905 FITTING, H., Das Wasserversorgung and die osmotischen Driickverhaltnisse der Wi stenpflanzen. Zeitschr. f. Bot. 3 : 209-275, 1911 HARRIS, J. A., GORTNER, R. A., and J. V. LOWRENCE, The relationship between the osmotic concentration of leaf sap and height of leaf insertion in trees. Bull. Torr. Bot. Club., 44:44, 229-286, 1917 HARRIS, J. A., LOWRENCE, J. V. and R. A. GORTNER, The crysoscopic constants of expressed vegetable saps as related to local environmental conditions in the Arizona deserts. Physiol. Res. 2: 1-49, 1916 ILJIN, V. S., Die Regulierung der Spaltoffnungen im Zusammenhang mit der Veranderung des osmotischen Driickes. Bot. Centralbl. Beihefte Nr. 32, 15-35, 1914 ILJIN, V. S., P. NAZAROVA, and M. OSTROVSKAJA, Osmotic pressure in roots and in leaves in relation to habitat moisture. Journ. Ecol. 4: 160-173, 1916 STANGE, B., Beziehungen zwischen Substratkonzentration, Zurgor and W achstum bei einiger Phanerogamen Pflanzen. Bot. Zeit. 50: 253-450, 1892 LIVINGSTON, B. E., The relation of the osmotic pressure of the cell sap in plants of arid habitats. Pl. W. 14: 153-164, 1911 URSPRUNG, A. and BLUM, G., Uber die Verteilung des osmotischen Wertes in der Pflanzen. Ber. deut. Bot. Ges. 34: 88-104, 1916, Uber die periodischen Schwankungen des osmotischen Wertes. Ber. deut. bot. Ges. 34: 105-123, igi6, Uber den Einfluss der Aussenbedingungen auf den osmotischen Wert. Ber. deut. bot. Ges. 34: 123-142, 1916