CH, VI] PLASMOLYSIS. 135 



grown but little, then comes a region where growth is 

 more vigorous, and further back growth again becomes 

 less marked. 



(174) Grand period, time observation. 



The grand period may be observed with bean roots, 4 

 or 5 being measured simultaneously. The experiment 

 should be started when the roots are 5 mm. in length, 

 and the length measured from a mark on the cotyledon. 

 A measurement is to be made every day at a given hour. 



Or a scale may be fixed parallel and close to the root 

 and the daily increment noted by reading off the position 

 of the tip of the root on the scale. 



(175) Growth and plasmolytic shrinking. 



De Vries' has shown that in many cases the shrinking 

 produced by plasmolysis is distributed in space in the 

 same way that growth is distributed. In other words, 

 that region of a plant-member which is growing most 

 quickly, shrinks most when plasmolysed. But this appears 

 not to be universally the case, as Schwendener and 

 Krabbe" have shown. The most striking exception to 

 the parallelism between growth and plasmolytic shrinking 

 is afforded by roots. 



Mark a bean root at 5, 10, 15, 20 mm. from the apex 



and place it in 10 p.c. NaCl solution until completely 



flaccid. On remeasuring it will be found that plasmolytic 



shrinking extends considerably further back than (as we 



know from exp. 171) growth is found to occur. 



1 Zellstreckung, 1877. 



^ Pringsheim's Jahrbiieher, xxv., 1893, p, 323. 



