870 MR. A. J. EWART ON ASSIMILATORY INHIBITION. 
of the leaves are killed ; and even those which remain living and 
show plasmolysis on moistening may have their vitality so in- 
juriously affected that they die without any return of assimilation 
taking place. One fact may at once be noticed, though it will 
appear again and again in the future experiments, and that is, 
that the stoppage of assimilation does not involve any percep- 
tible change whatever in the assimilatory apparatus. Of two 
cells of precisely similar microscopical appearance, one may be 
assimilating and the other not. 
The table is more of value as showing the extreme resistance 
which some Mosses show in the dried condition to short periods 
of heating at high temperatures, than as showing any marked 
production of assimilatory inhibition. Thus in Grimmia and 
Orthotrichum living cells may still be present after heating for 
6 hours to 90°C., and may remain living for some days though 
they have lost all power of assimilation and recovery. In order 
to obtain the full resistant power of the plants, the air in which 
they are heated must be perfectly dry. This is well shown by 
the increased resistant power shown by Grimmia conferta under 
the conditions of the following experiment :—Desiccator dried 
plants are heated in a CaCl, desiccator for 6 hours at 95°C.; 
after moistening, a few of the younger leaves and leaf-cells are 
found to be living and plasmolysable, but show no assimilation 
and no recovery. On planting, however, a few plants form new 
sprouts, z. e. under these conditions the plant withstood a tempe- 
rature 5^ C. higher than in the Table A. That the presence of 
oil has little or nothing to do with the power of resistance to 
heat is shown by the fact that Dicranum, the protoplasm of 
which contains plenty of oil, is not more resistant, and is in 
many cases less resistant, than other Mosses in which such oil is 
absent. 
It must be remembered that whenever Assimilation is said to 
be absent, what is really meant is that under optimal illumination 
in the presence of CO, no evolution of Oxygen can be detected. 
Assimilation and evolution of Oxygen are not necessarily 
synonymous, very weak assimilation may be masked by the 
concomitant respiration. Boussingault * and Holle t state that 
green leaves in darkness evolve from jl to jy the amount of 
* Boussingault, * Agronomie, Chimie Agricole et Physiologie,’ vol. iv. 1868, 
p. 329. 
t Holle, in * Flora,’ 1877, pp. 162 and 186. 
