62 CARNEGIE INSTITUTION OF WASHINGTON. 



ascribed to simple modifications of hydration, but it is highly probable that 

 flocculations and reversal of phases are concerned. 



Effect of Salt Solutions on Hydration and Swelling of Plant Tissues, 



by F. T. McLean. 



The swelling of plant tissues when in contact with solutions is a resultant 

 of a number of processes — osmotic pressure, hydration of the protoplasm 

 and cell-wall, chemical changes in the plant constituents, etc. By using 

 solutions which cause definite reactions with colloids similar to those in plant 

 tissues or with certain groups of constituents of plants, it is possible to obtain 

 indications of the importance of these substances to the maintenance of 

 turgidity in plants and consequently to growth. With this end in view, 

 young tissues of cactus {Opuntia discata) joints and of walnut (Juglans major) 

 and blackberry (Rubus vitifolius) stem-tips were immersed in solutions of 

 saponin, alanine, sucrose, d-glucose, and certain mineral salts, and their 

 swelling recorded by means of the auxograph. 



The concentrations of saponin tested (0.04 to 5.0 per cent) all caused rapid 

 swelling of Opuntia tissues. This was followed by pronounced shrinkage to 

 less than the original thickness. No shrinkage occurred in control sections 

 swelled in distilled water. In 1 per cent and in 5 per cent saponin Merck, 

 swelling was less than in water. Similar concentrations of saponin caused the 

 same kind and amount of swelling of blackberry sections as did water, without 

 subsequent shrinkage. Since saponin is a solvent for lecithin, the effects 

 on Opuntia may be due to the solution or displacement of a lecithin layer in 

 the plasma, thus rendering the cells more permeable to certain constituents 

 and permitting exosmose and shrinkage. If this be the case, then the black- 

 berry tissues either did not possess a lecithin layer or the permeability of the 

 plasma to the principal osmotically active constituents was not affected by 

 the removal of such a layer. 



Low concentrations (0.03 M or less) of alanine, sucrose, and glucose had 

 no marked effect upon the swelling of Opuntia or blackberry tissues. Sucrose 

 caused shrinkage (plasmolysis) of Opuntia tissues at a concentration of less 

 that 0.2 M, glucose at between 0.2 M and 0.3 M, KC1 at 0.15 M, and KN0 3 

 at 0.15 M or slightly less. Opuntia tissue swelled in 0.2 M glucose, which is 

 approximately isosmotic with the other solutions used, and it may therefore 

 be concluded that glucose is more readily absorbed than sucrose, potassium 

 chloride, or potassium nitrate. 



A comparison of the swelling of walnut tissues in chlorides of potassium, 

 sodium, magnesium, and calcium at 0.01 M concentration resulted in least 

 swelling of the tissues in potassium, as compared to distilled water, and 

 greatest in calcium. Another comparison of sulphate, chloride, and nitrate 

 of potassium at 0.01 M gave the least swelling, both of blackberry and of 

 walnut in sulphate (0.3 and 0.5 respectively of the swelling in water), and 

 most in nitrate (1.1 to 2.1 compared to water). These effects of the kations 

 and anions suggest that the aggregation of the plasma by nitrates and calcium 

 salts, respectively, increase its efficiency as a semipermeable membrane, and 

 thus permit great swelling due to osmotic pressure of the cell solutes. 



Tests of the longitudinal swelling of young blackberry-stem tissues gave 

 a quite different result for the chlorides of potassium, sodium, and calcium. 



