MR. A. J. EWART ON ASSIMILATORY INHIBITION. 395 
the shock induced by the sudden change of temperature, causing 
a temporary stoppage of assimilation, for in normal actively 
assimilating preparations the evolution of oxygen is not per- 
ceptibly affected by sudden changes of temperature for short 
periods of time, provided that the range lies within the critical 
points. ‘The phenomenon is probably simply due to respiration 
increasing more rapidly than and temporarily overpowering 
assimilation. 
The main results obtained by experimenting with freshwater 
alge, &c. are given below, and show that these plants are not 
very resistant to cold, all those examined being killed by being 
frozen. 
TaBLe K. 
- | 8 days ing 2° C. 
3 days at 09:5 C. to 2? C. hO Ce c 
| 
{ 
| 
—| 
(Edogonium | Nearly all filaments living. | No evol” of O (at 1? C.); | 
species ? No evol” of O. weak in| 4h. at 20° C. weak and in| 
1 h. at 20° C, fairly active | 3h. active. 
in 3 h., about normal in | 
5h 
Spirogyra | Most filaments dead, few Most filaments living. No, 
species ? living, plasmolysable and | evol® of O (at 1° C.), in 
with normal Chl. bands, | 1l h. at 209 C, weak, in 3 h. 
but these do not recover | about normal assim., in all | 
and soon die. living cells. | 
l 
Chara, No assim. or rotation. Most Nitella flexilis.—Slow rotation | 
Sragilis. end cells dead, nearly all| in older axial cells only. 
cortical and medullary cells! No evol? of O (at 1° c). 
living. In 15 min. at 20? C. | Evol” of O, shown first by 
veay weak evol” of O, but | the younger branches in | 
no rotation. Rotation com- | which rotation is still slow. 
mences in l h., and in 3 h. | In h. at 20? C. rotation | 
both it and assim. are and assim. active. 
active. 
With freshwater plants even after exposure reaching nearly to 
the critical point, no very marked after-effect is produced upon 
assimilation. This is probably because, owing to their slight 
powers of resistance to cold, the temperatures to which they can 
be exposed without being permanently injured are necessarily 
relatively high. It is very difficult, if not impossible, to cause 
even by very prolonged exposure to cold a stoppage of rotation 
in the larger axial cells of Nitella without their being permanently 
injuriously affected, and probably the same is the case with the 
LINN. JOURN.—BOTANY, VOL. XXXI. 2r 
