384 True. — On the Influence of Sudden Changes of 
is the result of a change of medium as well when this change 
calls forth an increased, as when it calls forth a decreased 
turgor-pressure. The conclusion follows that here the rate 
of growth stands in no direct proportion to the turgor-pressure. 
This is in accordance with the fact lately demonstrated by 
Pfeffer 1 , that turgor is not necessary for the growth of the cell- 
membrane. 
To point out the causes of this is no simple task. For 
greater clearness, let us consider the two cases separately. 
In the case of a change from a saltpetre solution to water, 
it is plainly impossible that the diminished growth-rate should 
have for its cause a lack of turgor-pressure. Abundant evi- 
dence from other sources shows that a reduced growth-rate 
can accompany an increasing turgor-pressure. Wieler 2 , Stange 3 , 
and Eschenhagen 4 may be cited in this connexion. Hegler 5 
found that a mechanical pull in the direction of the long axis 
of a plant caused a diminished rate of growth and an increased 
turgor. 
It seems that we have here a plain exhibition of proto- 
plasmic irritability. The change of concentration acts as a 
stimulus, which calls forth a reaction in the form of a diminished 
rate of growth. 
A number of possible causes of the diminished growth-rate 
succeeding the sudden change from water to the salt-solution 
suggest themselves. 
(1) Perhaps the return of full growth is delayed until 
a necessary minimum turgor-pressure is established. The 
period of retarded growth, as seen in roots of Vicia Faba , 
suddenly brought into a 1 per cent, solution of KN 0 3 , lasts 
usually from to 3^ hours. Whether such a period is 
necessary for the turgor-adjustment does not appear, the time 
relations of this change not having received especial attention 
1 Pfeffer, Druck u. Arbeitsleistung, p. 429. 
2 Wieler, Plasmolytische Versuche mit unverktzten Phanerogamen, Ber. d. 
deutsch. bot. Gesellsch. 1887, p. 375. 
3 Stange, loc. cit. 4 Eschenhagen, loc. cit. 
5 R, Hegler, Ueber den Einfluss des mechanischen Zuges auf das Wachsthum der 
Pflanzen. Cohn’s Beitr. z. Biol. d. Pflz., Bd. VI, Ileft 3, p. 1. 
