404 MR. A. J. EWART ON ASSIMILATORY INHIBITION, 
of H and CO,, the preparations also finally lose the power of 
assimilation. 
Moss-leaves, however, under these conditions retain the power 
of assimilation for an indefinite length of time. The explanation 
is that, in the first two plants under these abnormal conditions, 
a state of assimilatory inhibition is induced in the exposed 
specimens, from which at first recovery is possible if the plants 
are brought under normal conditions again, č. e. on exposure 
to air after a longer or shorter latent period the power of 
assimilation returns. If the exposure has been too prolonged, 
the power of recovery is lost and the preparations finally 
die. 
If green plants are exposed to light in an atmosphere of H, 
at the end of severa] hours’ exposure the surrounding gas is found 
to have undergone no perceptible change in composition, but 
nevertheless during the whole time of the exposure both assimi- 
lation and respiration are going on, and the specimens are con- 
tinuously evolving traces of both oxygen and CO,, which may 
be detected by the Bacterium method and by Phenolpthalein 
respectively. 
In an atmosphere of pure CO, in all cases, assimilation and 
evolution of oxygen cease almost immediately (in 1 to 2 minutes). 
If the CO, is now replaced by H, a normal evolution of 
oxygen is at once shown, but if the preparations are kept in an 
atmosphere of CO, for some time they may only recommence 
to evolve oxygen and assimilate after a longer or shorter period 
of time has elapsed. In an atmosphere of CO, moss plants may 
remain living for many days or even weeks, but Chara or Elodea 
cease to show rotation after 15 to 20 minutes or 5 to 10 minutes 
respectively, and after 2 or 3 hours’ immersion are killed ; whereas 
in an atmosphere of pure hydrogen Chara may remain living for 
half a day (12 hours). In an atmosphere of hydrogen rotation 
gradually becomes less and less rapid, but when suddenly sur- 
rounded by CO, rotation undergoes an immediate diminution to 
as much as one half its previous velocity, the difference being due 
to the fact that in the latter case, besides the removal of the 
necessary oxygen, a direct and immediate poisonous and retarding 
influence is produced. 
Mosses, however, as well as many plants of lower organization, 
are remarkably resistant not only to the asphyxiating effects 
of immersion in an atmosphere of hydrogen, but also to the 
