DR. A. J. EWART ON ASSIMILATORY INHIBITION. 573 
in them by starvation, as well as by the absence of light. Green 
leaves of Elodea canadensis kept in darkness in weak sugar 
solution remain green, and may retain the power of assimilation 
for weeks. Finally, it begins to weaken, and after 2-3 months, 
though in many parts green and apparently normal chlorophyll 
grains may be found, in no case can any power of assimilation be 
detected. Such parts, however, may, on re-accustoming to water, 
remain living, and finally resume their normal function. In this 
case the loss of the power of assimilation cannot be a pheno- 
menon of starvation, but is probably directly due to the enforced 
continual functional inactivity of the chloroplastid, finally inducing 
in it a condition characterized by a temporary or permanent 
inability to assimilate. 
Conclusions. 
Chloroplastids developed in darkness, whether they become 
green or are etiolated, may possess a fairly active power of assi- 
milation corresponding to their size and depth of coloration. 
The power of assimilation is absent whilst the etiolated leaf is 
still quite young, and finally disappears again after the leaf has 
been kept for a long time in darkness, even though abundant 
supplies of food-material may be present.  Etiolated leaves 
exposed to light in an atmosphere deprived of all CO, turn green, 
and may acquire a quite active power of assimilation, which, 
however, soon begins to weaken and is in most cases rapidly lost. 
The stoppage of assimilation may take place whilst the chloro- 
plastids are still normal in appearance; but in all cases a visible 
change in appearance and coloration is finally produced. From 
the first condition recovery is generally, but from the second only 
rarely, possible. Assimilatory cells or tissues, therefore, which 
are prevented from assimilating by being kept in darkness, or by 
being exposed to light in an atmosphere deprived of all CO,, 
retain their potential power of assimilation only for a given 
length of time, which is, the other conditions being similar, shorter 
in the latter case than in the former, and which is in each case 
mainly dependent upon the hereditary nature of the given plant. 
Note on the Effects of Exposure to Sunlight upon Chara. 
My attention has been called by Prof. Pfeffer to certain 
peculiarities exhibited by a culture of Chara hispida, Linn., which 
during July and August 1895 was accidentally exposed in a 
