298 BOTANICAL GAZETTE [OC1OBER 
I and II. Ev denotes an uncovered culture with rapid evapora- 
tion. 
TABEE FV- 
POROUS PLATE CULTURES. 
Solution Original hes onse Time Solution Original Response Time 
form. P ; " i. form. P . : 
biiacd 3% 
100 L P Sp. F. 9 ay K ig Be 10 
8 . 42a x 
ee S P Sp. F. 9 a. 5 | Sp. F; 9 
pn | 4m 
<a 8 12 Sp. F: 10 — K Pete 16 
—-K F P. F. 10 SL, P P. 16 
Io 10 
<2 L P Sp. F. 9 Te L P P. 46 
Io roo 
= K F P. FE; 10 «= |i L, Ev] F Is 6 
fe) roo 
4. GELATINE CULTURES. 
These were made like the plate cultures just described, 
excepting that in the place of the porcelain support the solution 
to be used was thickened with gelatin until it would give a firm 
surface on which to place the alga. The result was uniform with 
the foregoing. The gelatin itself has no influence. The osmotic 
pressure of the solution determines the response of the organism. 
Gelatin cultures cannot be continued very long because of bac- 
terial action, and are therefore not very satisfactory. 
5. CULTURES IN DARKNESS. 
In darkness the alga remains green and healthy for three to 
five weeks. At last the cells become plasmolyzed and go to 
pieces. Putting the culture in darkness has no effect whatever 
upon the response of the plant. This probably indicates that 
the mechanism of polymorphism is not connected with that of 
photosynthesis. 
6. EVAPORATION CULTURES. 
Weak solutions, with their contained filaments, may be left 
open to the air, and within a few days become very much con- 
centrated through evaporation. The response of the plant 1s 
