IN VEGETABLE BIOLOGY. 871 
stopped in the dark if light have imparted sufficient impetus to 
the plate. 
(9) In darkness the plate may turn so as to remain either 
face up or on its edge. The position ultimately assumed depends 
on the accumulated (potential) effects of light. — " 
On Chlorophyll Figures. (Preliminary Notice.) 
It was stated in the former memoir that prolonged insolation, 
as Stahl showed, causes the chlorophyll to mass in the corners 
of the cells (mesophyll of Oxalis Acetosella* &c.). It was also 
shown that the same thing occurs upon long-continued with- 
holding of light; and when remarking on this, in connection with 
Eschscholtzia californica, it was noted that the grains lie so closely 
together as to be liable, but for their colour, to be taken for local 
thickenings of the wall—a very different state of things from that 
portrayed by Stahl, where the grains, although near together, are 
far from being so closely crowded as to give this impression. Had 
Stahl continued the insolation, he would have found that these 
massed grains touch and then adhere to each other (“ cohesion ”), 
and might further be so firmly welded together as apparently to 
lose their individuality—thus exhibiting what it is proposed to 
call “ coalescence.” ‘ 
Senecio vulgaris is a very good type for the study of this 
curious phenomenon; the only requisite is brilliant day with 
sunshine (for five or six hours) as strong and unintermittent as 
possible. Fig. 23a shows a Nostoc-like chain of cohering 
granules seen, in bird’s-eye view, lying across the lumen of a 
palisade-cell of a S. vulgaris set for several hours in strong, but 
in this case intermittent, sunlight. Cohesion is here very well 
Pronounced ; but it is doubtful if coalescence has set in, for there 
Were dark lines between the grains, except in one instance, it is 
true: whether, however, this latter is a result of coalescence, or 
is à representative of a single grain in course of division, it is 
Impossible to say. From the palisade-tissue was also derived 
fig. 235, where the sun’s action has led to the formation of an 
Ophiocytium-like mass of chlorophyll in wbich cohesion was 
Plainly betrayed, but in which I failed to obtain satisfactory 
evidence of coalescence, except at the narrow portion, where it 
* Stahl, Bot, Zeitung, 1880. The figure alluded to is well known from its 
reproduction in the general works of Sachs and Pfeffer. 
