IN VEGETABLE BIOLOGY. 231 
crease of illumination ; and 8rd, lowering of protoplasmic tone— 
the last two being the result of sectioning. It does not appear 
that 5-per-cent. solutions of sugar exert much, if indeed any, 
lowering action upon the protoplasm of intact organs; at least this 
applies to uninjured Elodea-plants both in the dark and in dif- 
fused light. After three days the chlorophyll of leaves from 
specimens grown in sugar-solution may show slight tendency to 
apostrophe; but this is not always the case by any means. 
On the assumption by Chlorophyll Grains of profile position with 
respect to the wall upon which they are placed. 
It becomes necessary to contest the correctness of another of 
Stahl's views. He remarks*, à propos of Elodea canadensis, that 
when the chlorophyll grains run together into clumps on ex- 
posure to direct sunlight, the greater number, especially those 
lying at the outskirts of the clumps, are tilted up so as to present 
their edge to that wall of the cell upon which they are ranged. 
Stahl considers that this is brought about by spontaneous move- 
ment of the grain upon its own axis, its object being to save the 
grain from broadside illumination. Here, however, he is quite 
in error. It is, indeed, the fact that such set-on-edge grains are 
to be seen in the cells of Elodea-leaves exposed to sunlight and 
high diffused illumination ; but I have never found any large pro- 
portion of the grains of a clump in this position, and with regard 
to those so placed, it is easy enough by careful examination to 
ascertain how the state of things was brought about. It has 
already been mentioned that, when leaves of Elodea are exposed 
for a few minutes to strong sunlight, one may often see two 
grains start from opposite sides of a cell, run along the inter- 
vening bridge of plasma and clash, one of them turning upon its 
edge while the other remains upon its side, and that the grains 
_ are in this way enabled to pass each other. A grain thus forced 
upon its edge may either remain so until it reaches and glides 
upon the side-wall without shifting upon its axis, or it may 
Strike another grain or group of grains, and in consequence either 
turn over broadside again or remain upon its edge, pressed 
closely against the obstacle. It is safe to affirm, therefore, that 
the grains which Stahl speaks of did not, as he thinks, sponta- 
neously turn on their edge (he does not profess to have seen 
* Bot, Zeitung, 1880, p. 337. v2 
