148 PLASMOLYSIS. [CH. VI 



(175) Growth and plasmolytic shrinkmg. 



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. 



We find that a convenient method of measuring the 

 distance between marks is the following. The root is 

 laid on wet blotting-paper to prevent it withering and is 

 supported on a table sliding in a horizontal slot, on which 

 a millimeter scale with a vernier is engraved. A small 

 reading microscope with cross wires is fixed vertically 

 above the root, the table is pushed along the slot and the 

 vernier is read as each mark on the root comes under the 

 cross wires. We thus read to 0*1 mm. with fair accuracy. 



1 Zellstreckung, 1877. 



' Pringsheim's Jahrbiicher, xxv. 1893, p. 323. See also Sachs, in his 

 Arbeiten, i. p. 396. 



