MR. A. J. EWART ON ASSIMILATORY INHIBITION. 451 
living but non-assimilating cells, in which the chlorophyll grains 
are but little smaller than normal; and though many have a 
brown or brownish-green coloration, many are merely yellowish 
green and more green than yellow. On re-exposure to light, 
chlorophyll grains reduced to J their normal size and quite brown 
or yellowish brown, became green and of normal size in 10 to 30 
days. If the reduction has gone further than this, no recovery 
or regeneration takes place, and in water such cells soon die, 
though in a nutrient solution they may remain living for days 
or even weeks without any further change taking place. As 
recovery takes place, many cells with chlorophyll grains 1 to 4 
normal size, and still quite yellowish brown, may show distinct 
but weak assimilation ; most cells with the chlorophyll grains 
$ normal size, and brownish or yellowish green, show a mode- 
rately active power of assimilation. The stoppage of the power 
of assimilation is not merely due to the change in colour of the 
chlorophyll grains, butis primarily due to some internal invisible 
alteration, of which the change in the colour of the chlorophyll 
grain is the outward and visible sign; for on re-exposure to 
light, a weak power of assimilation may return before any per- 
ceptible alteration in either the size or the colour of the chlo- 
rophyll grain has taken place. 
In plants kept in 20-per-cent. sugar solution the same degen- 
erative changes take place, but only with from 3 to ] the rapidity 
under the most favourable conditions with which it occurs in 
darkness in water. In sugar solution the degenerative changes 
are much more rapidly produced when the plants are exposed to 
bright light, with an abundant supply of oxygen, than when kept 
in the darkness and imperfectly aerated. Under the latter con- 
ditions, after two months the chlorophyll grains may be still green 
and apparently normal, but show no power ot assimilation. 
Under the former conditions, cells in which the chlorophyll grains 
are reduced from 4 to $ their normal size and are brownish 
green in colour, generally show a distinet though weak power of 
assimilation ; but assimilation is always absent when the chlo- 
rophyll grains are quite brown and small. The same phenomena 
of recovery are shown as previously if the plants are accustomed 
to weaker solutions, and finally to water. f 
The degenerative ehanges indueed in the chlorophyll bodies by 
keeping the plants in darkness in water are undoubtedly star- 
vation phenomena, the material used in respiration beiug supplied 
