MR. A. J. EWART ON ASSIMILATORY INHIBITION. 419 
3 minutes; in neutral meat-extract or in a boiled watery extract 
of moss-leaves it takes 15 to 20 minutes longer to come to rest ; 
whilst in the neighbourhood of dying cells which have been 
suddenly fatally injured the movement may continue, provided 
the cell was previously actively assimilating, for as long as 
2 hours, and is independent of light. Cells killed by asphyxia- 
tion and non-chlorophyllaceous cells show no evolution of oxygen 
on death. The possibility of a slight evolution of oxygen taking 
place in many cases coincidently with death does not necessarily 
involve the assumption of the presence of a special oxygen- 
producing substance in the living assimilating cell. The slight 
amount of oxygen set free may have been held iu a state of loose 
combination by the protoplasm, or the phenomenon may be a 
purely physical one, the actively assimilating cell when suddenly 
killed continuing for some time to slowly diffuse out the oxygen 
with which its substance was previously saturated. 
Pringsheim's statement that recovery from inanition will not 
take place if the plants are exposed to light in an assimilatory 
mixture of hydrogen and CO,, but only when free oxygen is 
admitted, is not true in the case of Mosses. The phenomena 
he observed in support of this contention, with Chara, can 
readily be explained when we remember that the inhibition of 
assimilation caused when inanition is produced will necessarily 
be followed by a longer or shorter latent period, and if we 
suppose that the addition of free external oxygen exercises 8 
stimulating influence and shortens the latent period of recovery. 
The conditions as regards the absorption and evolution of oxygen 
are very different in an atmosphere of hydrogen containing a trace 
of CO, (such as Pringsheim experimented with) to what they are 
in ordinary air. In such an atmosphere, the oxygen's partial pre- 
sence being nil, the cell will rapidly evolve all dissolved oxygen it 
may contain, an abnormal condition being thereby produced. This 
ds shown by the fact that in preparations of Chara, even though 
exposed to continuous illumination, in a current of Hydrogen + a 
trace of CO,, which continually removes from them all oxvgen as 
fast as it is formed, inanition is finally produced and assimilation 
and rotation cease. Moss-leaves, however, under such conditions 
retain the power of assimilation for an indefinite length of time. 
Engelmann * explains the phenomena on which Pringsheim’s 
* “ Die Purpurbakterien und ihre Beziehungen zum Licht,” in Bot. Zeit., 
Oct. 1888, p. 717. 
