MR. A. J. EWART ON ASSIMILATORY INHIBITION. 457 
Catharinea undulata.—L. Y. Apical 2, chlorophyll grains 3 to nearly full size, 
and quite active evolution of oxygen. Basal 1, chlorophyll grains about 
+ normal size, and weak evolution of oxygen*. L. }, Apical portion, 
very weak evolution of oxygen, and chlorophyll grains 1 to 1 normal 
size. L. s. Chlorophyll grains abundant, green, and from } to } normal 
size in apical š of leaf, but no evolution of oxygen, though the chlo- | 
rophyll grains twice as large as, and in relation to the protoplasm in | 
greater amount than, in the base of the leaf, L. 1. 
A careful study of the above results enforces the conclusion 
that, although the presence of a certain amount of chlorophyll 
is necessary before any evolution of oxygen can take place, 
nevertheless, in determining the development of the power of 
assimilation and the stage at which an evolution of oxygen is 
possible, equally important factors, of probably plasmatie origin, 
also enter iuto play. The leaves of Phanerogams and Mosses and 
the gemme of Marchantia are parasitic upon their parent plants 
for only a relatively short period at the commencement of their 
existence; for so soon as they show any evolution of oxygen, and 
this takes place at a comparatively early stage of their life- 
history, the power of assimilation is greater than that of respira- 
tion, aud though at first, when the power of assimilation is 
still very weak, the substance gained during the day may be 
counterbalanced or more than counterbalanced by that lost by 
respiration during the night, very soon the amount gaiued by 
assimilation far surpasses that lost by respiration, and the leaf, 
instead of drawing supplies from the parent plant, sends supplies 
to it. 
With moss-leaves it is especially noticeable that in the apical 
portion of the young leaf, which is more exposed to light and 
to contact with air, the chlorophyll grains iucrease more rapiuly 
in size and the power of assimilation is sooner developed than 
in the more shaded basal portion of the leaf. The same 
* In full-grown leaves of Catharinea the chlorophyll grains at the base of 
the leaf are much smaller (} to } and from } to } in relation to the size 
of the cell) than those in the rest of the leaf; the evolution of oxygen is 
correspondingly weaker, and is in some cases almost imperceptible. The 
cells at the base of the leaf seem to have, owing to their less exposed position 
and to their forming the channel of communication between the leaf and the 
stem, as much a conductory as an assimilatory function, and are especially 
liable to have their assimilatory powers still further diminished by an over 
accumulation of carbohydrates. 
