426 MR. A. J. EWART ON ASSIMILATORY INHIBITION. 
oxygen previously present in the chlorophyll grain, nor is the 
movement of the Bacteria due to the evolution of nutritious 
substances from the chlorophyll grain, for in a solution of sugar 
the Bacteria come to rest as soon in the neighbourhood of dying 
cells or grains as in the open field. 
To detect the evolution of oxygen, chlorophyll grains quite 
free from adhering protoplasm are better than ones to which 
plasma is attached. The dying but still respiring plasma absorbs 
oxygen, and this is the case even with the free entire (but fatally 
affected) cell-contents ; such show in sugar solution no evolution: 
of oxygen and no movement of Bacteria in their neighbourhood 
(previously to examination the plants were in all cases kept for 
one to a few days in darkness, or semi-darkness). Rarely the 
complete uninjured cell-contents may be obtained lying free. 
These show a distinct power of assimilation which may continue 
for several hours, and in a few cases for more than a day. 
In the cell with Bacteria the chlorophyll grains may die 
because of the abnormal conditions (absence of oxygen, presence 
of Bacteria) to which they are exposed in the closed cell. Pre- 
parations of chlorophyll grains, however, kept in a hanging drop 
of sugar solution in a dark chamber for several hours are found 
to show no evolution of oxygen on examination ; z. e. the chloro- 
phyll grains are either unable to recover from the shock of 
removal and isolation, or are incapable of continuing a separate 
existence apart from the cell to which they belong for longer 
than a few hours, their autonomy being only partial and incom- 
plete. 
In other media than sugar solution similar or worse results 
are given. Sugar solution+1 per cent. peptone or with a little 
gum arabic gives similar results to sugar solution alone, whilst 
the viscidity of egg-albumin stops or so retards the movement of 
the Bacteria as to prevent its being used as a medium. 
In Selaginella, owing to the plants having been previously 
kept in the darkness for 2 or 3 days, the chlorophyll grains show 
no perceptible starch. The isolated chlorophyll grains, after 
showing 10 hours’ assimilation, on staining with iodine show very 
minute granules of starch, but not always. These might, how- 
ever, have been originally present, but invisible until stained, or 
might be formed from the sugar solution in which the grain lies. 
In preparations kept in darkness for the same time, however, no 
formation of starch can be detected. In Vallisneria a similar 
