IN VEGETABLE BIGLOGY. 375 
negative) of mesophyll and palisade chlorophyll is merely a phe- 
nomenon of fragmentation? If so, the whole matter should 
perhaps be viewed somewhat in this way :—In diffused light of 
medium strength the previously aggregated protoplasm spreads 
itself out upon the cell-wall, moving in the direction of least 
resistance to do so. [Upon this point see also p. 380.] Should 
this direction be such that the aggregates are drawn towards one 
another, the chlorophyll not being differentiated from the proto- 
plasm, coalescence ensues, and a single chlorophyll body is formed 
in each vell (Selaginella, Draparnaldia) ; but if the chlorophyll 
has undergone differentiation from the protoplasm, release of 
the latter from pressure must clearly be followed by separation 
of the several chlorophyll masses. 
Mention should here be made of the late Charles Darwin's* 
discovery of the “aggregation” of chlorophyll grains of Dio- 
n@a muscipula and other types upon their exposure to weak ` 
solutions of ammonium salts. Darwin has furnished evidence 
tending to show that the grains, even when aggregated beyond 
all possibility of individual recognition, can be regenerated—a 
proof that any changes caused in the grains themselves by the 
salt cannot be very far-reaching. Is it possible that proto- 
plasmie movement is at the bottom of this, as it is of the coales- 
cence in sunlight and darkness? An enhanced rate of stream- 
ing was directly observed by Francis Darwint and by H. de 
Vries f in the cells of Drosera tentacles lying in solutions of car- 
bonate of ammonia; and should the streams converge towards 
certain points, it 1s easy to understand how the grains would be 
driven into a heap, and thus prepared for bécoming firmly welded. 
Perhaps in this case, and also when coalescence ensues in sun- 
light or darkness, contact induces some slight change in the 
grains whereby they become weldable, as impacts of relatively 
great violence without any supervening coalescence can occur 
between grains of Elodea canadensis suddenly set in bright sun- 
light. But the whole subject is as obscure as it is interesting. 
* Journ. Linn. Soc., Bot. vol. xix. p. 266. 
t Quart. Journ. Microse. Sc. 1876, p. 309 &e. 
1 Bot. Zeitung, 1886, p. 1 &c. 
