372 MR. A. J. EWART ON ASSIMILATORY INHIBITION. 
one which remains in damp air attached to the parent plant, and 
in some cases may not take place at all. In water Bacterium 
Termo is to be regarded simply as an absorber of oxygen and 
producer of CO,. That in water it exercises no other injurious 
poisonous influence upon the leaf-cells is shown by the long 
period of time during which a moss-leaf may remain living in a 
closed cell with Bacteria. Similarly the shock of removal from 
the parent plant is so slight as to be negligible. Hence the 
slower recovery of the separated leaf in a closed cellis due partly 
to the lack of oxygen, and perhaps partly to deficient nutrition. 
The return of assimilation and recovery of the leaf need not 
necessarily be followed on the same leaf, but can be traced by 
making successive preparations at given intervals of time from 
neighbouring leaves. lt is the age and position of the leaf 
which determine its resistant power; each leaf behaves similarly 
to its immediate neighbours, though between the basal and 
apical leaves wide differences in behaviour and resistant power 
may exist. As regards dry heat and desiccation it is the young 
leaves which are most, and the old leaves least, resistant. As 
the adult leaves grow older, their resistant power to dry heat, 
as well as their assimilating powers, becomes lessened. 
To obtain good results, it is better to heat for a longer time at 
alower temperature. The results of such heating are shown in 
the columns of Table B, from which several interesting conclu- 
sions ean be deduced. A comparison between (a) and (b) and 
(c) and (d) shows that strong desiccation previous to heating 
lowers the plant's resistant powers, but that the drier the atmo- 
sphere in which the actual heating takes place the less is the 
plant affected. Columns c, d, and e show that the duration of 
the exposure is at least as important as the temperature to 
which the plant is heated, in producing a prolonged inhibitory 
after-effect upon assimilation. This after-effect is more readily 
produced in the older than in the younger leaves. Though it 
may take days before assimilation becomes quite normal, never- 
theless in the young leaves assimilation is rarely completely 
absent for more than a few hours. Under the same exposure à 
more prolonged inhibitory after-effect is produced in Dicranum 
than in Bryum and Orthotrichum. 
Table C gives tbe results obtaiaed with various Chloro- and 
Cyanophyceæ. The plants are collected as pure as possible, 
dried in bulk, and then kept in thin flakes on watch-glasses in 
