Turgor and of Temperature on Growth. 385 
as yet The few experiments bearing on this point give 
a very incomplete view of details. De Vries 1 states that out 
of 0-35 molecules of glycerine, 0-03 pass into the cell in one 
hour. Janse 2 found plasmolyzing substances in the cell-sap 
of Spirogyra after 30 minutes in either dilute or concentrated 
solutions. Eschenhagen 3 found that the hyphae of moulds, 
transferred suddenly from a 10 per cent, to a 40 per cent, 
sugar-solution, after 6 hours were plasmolyzed by a 30 per 
cent, sugar-solution, not yet having reached the concentration 
of the new medium. It is here to be noticed, however, that 
the increase in osmotically active substances is brought about, 
not by penetration of the sugar, but by metabolic activity in 
the cells themselves, and a different action may result. 
It seems entirely possible in the case under consideration 
that an interval equal to the retardation-period found, might 
be necessary for an adjustment of the turgor-pressure. If 
this should be the case, it would not be unexpected were the 
rate of growth during this period to show more or less dis- 
turbance. 
(2) In view of the exhibition of irritation seen to follow the 
reverse change of medium, it would seem highly probable 
that here a similar phenomenon might be present. 
(3) It seems possible that the medium may exert a specific 
chemical effect on the seedlings placed in it. Evidence sup- 
porting such a supposition is afforded only by roots that were 
left in the saltpetre solution for long periods of time. 
Recapitulation . 
Bringing together the most important results following from 
the experiments above presented, it appears (1) that a sudden 
and decided increase of the concentration of the liquid medium 
calls forth in growing roots a change of turgor-pressure, pro- 
ducing, or tending to produce, a mechanical contraction, also 
1 De Vries, cited by Stange, loc. cit. 
2 Janse, Plasmolytische Versuche an Algen, Bot. Centrafbl. XXXII (1887), 
Th. i, p. 21. 
3 Eschenhagen. loc. cit., p. 35. 
