220 MR. S. LE M. MOORE'8 STUDIES 
to different parts of the plant, nor to abnormal protoplasmic con- 
ditions, but to the normal state of every cell. The parietal zone 
consists of protoplasm toned so highly to light that the chloro- 
phyll embedded in it does not manifest, even in direct sunlight*, 
the slight movements of apostrophe and epistrophe ; whereas the 
inner zone exceeds the protoplasm of Elodea in sensitiveness to 
light as much as the latter does the protoplasm of ordinary types. 
This coexistence in the same cell of the extremes of mobility and 
of impassiveness is, despite its familiarity, a highly remarkable 
circumstance. 
On the Nature of the Movement of Chlorophyll Grains. 
Why do the chlorophyll grains move into positive apostrophe? 
Can it be, as Béhmt thinks, to avoid the destructive effects of 
light? If so, it is very remarkable that the position of the posi- 
tive critical point should be so variable in the photrum, not only 
as respects different types, but also different individuals of the 
same species and different parts of the same individual. Is it 
possible to believe that the chlorophyll of, for instance, the lower 
cell-layer of Elodea-leaves differs so much in constitution from 
that of the upper cells that it can without injury suffer exposure 
to light of intensity sufficient to destroy the upper chlorophyll? 
This consideration seems to warrant an emphatic negative to 
Bóhm's theory, quite apart from the objection urged against it 
by Stahl f, that before it can be said to be safely grounded, the 
onus is upon its upholder of proving that the grains are destroyed 
by sunlight if their apostrophization be prevented §. Stahl|| has 
himself fathered a hypothesis to the effect that the aim of apostro- 
phization of chlorophyll in sunlight is to prevent accumulation, 
to an injurious. extent, of the products of assimilation. Apart 
from the charge of embodying a discredited form of teleology 
* Pringsheim (Ueber Lichtwirkung und Chlorophyllfunction in der Pflanze, 
p. 933) found that in concentrated sunlight movements are excited in the 
parietal protoplasm, as is evidenced hy the grains shifting their position. 
Velten has recorded very slight movement in the parietal protoplasm (Oesterr. 
bot. Zeitsch. 1876, no. 3). 
t This is stated on Stabl's authority (Bot. Zeitung, 1880, p. 381). I have 
failed to find the reference in either of Bóhm's memoirs. 
1 Bot. Zeitung, 1880, p. 381. 
$ It is scarcely necessary to say that the behaviour of the grains in concen- 
trated sunlight, as observed by Feiugshetn, i is not in point. 
| Bot. Zeitung, 1880, p. 381. 
