PLANT PHYSIOLOGY PRESENT PROBLEMS 127 



of substances from without, or (2) by substances of strong osmotic 

 action produced within the cell through the stimulative action of 

 external agents. It was determined in this case that in general no 

 absorption of the substances bathing the plant occurs; therefore, 

 osmotic substances are produced within the cell and largely by in- 

 creased concentration of the normal organic cell products. The 

 extent and method of this capability for turgor regulation are highly 

 important, as is also the general question of the relation of turgor 

 to growth. In recent times some of the important problems in this 

 connection have been well suggested by the work of Ryssleberghe, 

 Puriewitsch, Overton, Copeland, and Livingston. 



The absorptive systems of plants seem to be admirably adapted 

 for their needs from a diosmotic point of view. Diffusion may, there- 

 fore, be sufficiently rapid to supply all demands of the absorbing 

 cells or organs. Nevertheless, the assumption that ordinarily diffusion 

 through the cell and plasmatic membrane is sufficiently rapid prop- 

 erly to provide for the translocation of metabolic products from cell 

 to cell is certainly open to further inquiry. Present knowledge of the 

 translocatory processes is insufficient. Plasmatic connections between 

 cells are now known to be of common occurrence, and this fact has 

 given further interest to the above inquiry. Brown and Escombe 

 are of the opinion that the plasmatic connections are eminently 

 adapted for all of those phenomena which they have found to belong 

 as subsequently mentioned, to multiperforate septa. They claim, 

 further, that with slight differences of osmotic pressure the necessary 

 concentration of gradient for increased translocation would be very 

 simply effected. 



Thus far it has been difficult to throw any light upon cell-absorp- 

 tion and selection in many complex natural relationships by calling 

 in the assistance of the dissociation theory and the ionic relationships 

 of the salts in the soil. The external relationships of nutrient salts, 

 or the relative abundance of these in substrata supporting vegetation, 

 constitutes a problem with which the physiologist must be concerned. 

 It is only necessary to glance at the results of work done by various 

 experiment stations in this country to be convinced of the great 

 physiological importance which may be attached to such studies. 



Recent results tend to emphasize the importance of considering 

 to a greater degree the physical conditions of the soil. Some have 

 even gone so far as to claim that practically all soils contain a suffi- 

 cient quantity of plant food, and that the all-important question 

 is the regulation of the water-supply in accordance with the quality 

 of the particular soil. This latter, however, is an error into which 

 few physiologists have fallen. Nevertheless, precise studies upon 

 the relation of plants to the physical characters of soils afford pro- 

 blems which should receive the best attention. Many of the pro- 



