INFLUENCE OF STREAMING ON OSMOTIC PRESSURE 15 



The leaf-cells of plants of Elodca kept in 10 to 20 per cent, sugar 

 solutions for two to three months in darkness may still contain appa- 

 rently normal and green chloroplastids, but show no streaming and no 

 power of carbon dioxide assimilation. On reaccustoming to water the 

 latter may slowly return in part, but not the former, whatever stimuli 

 are applied. Apparently the protoplasm has been brought to such a 

 condition of increased viscosity that streaming is no longer possible, but 

 in new leaves formed by apical growth it can readily be induced. 



SECTION 5. The Influence of Streaming on Osmotic Pressure and 



Diosmosis. 



There is no perceptible change in the osmotic pressure or in the 

 diosmotic properties as the result of the commencement of streaming in 

 a previously quiescent cell (E lode a, Vallisneria^ Trianea Bogotcnsis, Aristo- 

 lochia Sipho, Lepidium, Trade scantia). The osmotic pressure was tested in 

 the usual manner, and the diosmotic properties by immersal in very dilute 

 solutions of various aniline dyes. Actively rotating cells often accumulate 

 a dye, viz. methyl-blue, more rapidly than resting ones, but this may be 

 due to the presence of an increased percentage of substances in the cell- 

 sap, which cause the dye to be precipitated in a non-diosmosing form, viz. 

 tannate of methyl-blue. By treatment with dilute acid the dye may be 

 removed 1 , and the observations may be repeated on cells which have 

 ceased or which have commenced to rotate. Since an increase in the 

 rapidity of absorption (as well as an occasional decrease) may be shown in 

 both cases it is obviously unconnected with streaming, but is due to the 

 treatment with acid (or to the alteration or escape of certain constituents of 

 the cell-sap). Moreover, using methyl-violet and cyanin, which diosmose 

 away again in pure water, no constant difference in the rate of absorption 

 was perceptible between cells when rotating and when quiescent. The 

 presence of rotation does, however, seem to be indirectly connected with 

 a fall of the osmotic pressure in certain cases. Thus if leaves of Elodea are 

 kept in well-aerated water in darkness for five to ten days at 25 C. the 

 osmotic pressure in the rotating cells of a leaf may be less on the average by 

 1 or even -5 per cent. KNO 3 , or 1-5 to 4 per cent, cane sugar, than it is in 

 the quiescent cells 2 . This is probably due to the rotating cells consuming 

 more food materials and hence reducing the percentage of soluble sub- 

 stances in the cell-sap, but it might also be the result of increased 

 diosmosis. After more prolonged starvation all the cells fall to about the 

 same average osmotic pressure, and no constant difference is perceptible 

 between quiescent cells and ones which show, or have shown, rotation. 



1 Pfeffer, Unters. a. d. Bot. lust, zu Tubingen, 1886, Bd. n, p. 286. 



2 In individual cases the difference may amount to as much as I per cent. KNO S . 



