2l6 



PHYSIOLOGY OF GROWTH AND CONFIGURATION 



Experiments with plasmolysis were at first conducted only with single 

 cells, but de Vries' plasmolyzed entire plant organs during the period of en- 

 largement. He showed that when pieces of the growing region, of stems, roots 

 or flower-stalks, were placed in concentrated salt solution a considerable shorten- 

 ing was evident. This shortening is due to plasmolysis of the cells, and the 

 plasmolyzed pieces were always wilted and flaccid, but when they were returned 

 to pure water they regained their former length and rigidity. Mature organs, 

 however, whose enlarging periods were over, showed no shrinkage when placed 

 in strong salt solutions; the stretching caused by tiurgor had by this time 

 become fixed through further deposition of cellulose on or in the walls. 



Fig. 99. — Auxanometer. {After Pfeffer.) 



Turgor can thus produce enlargement of cells only when the walls are capable 

 of being stretched by the pressure that is developed. Experiments carried out 

 by Wortmann^ showed that the cell walls of young cells possess this quality of 

 extensibility in a much higher degree than do older ones, extensibility decreas- 

 ing gradually with advancing age. The ultimate loss of this quality of the 

 walls results in the termination of cell enlargement, even though turgor may 



' Vries, Hugo de, 1877. 1, «. (See note i, p. 113.] 



2 Wartmann, J., Beitrftge zur Physiologie des Wachsthums. Bot. Zeitg. 47 : 229-239, 245-253, 261-272, 

 277-288, 293-304. 1889. Schwendener, S., and Krabbo, G., Ueber die Beziehung zwisohen dem Maass 

 der Turgordehnung und der Geschwindigkeit der Langenzunahme Waohsender Organe. Jahrb. wias. Bot. 

 as: 323-369. 1893. 



