IN VEGETABLE BIOLOGY. 369 
The plate’s contraction in sunlight and the formation of lenticular 
bodies have already been adverted to (see p. 359). 
It appears, then, that in strong sunlight the chlorophyll plate 
is apostrophized, and that apostrophe makes way for epistrophe 
in diffused light and darkness. It might further be expected 
that negative apostrophe succeeds epistrophe, and clear indica- 
tions have been obtained in proof thereof. The effects of dark- 
ness on the plate are shown in figs. 22 5-d. Here fig. b is that 
of an apostrophized plate lying face up, the position it occupied 
before confinement: in fig. c apostrophe is more pronounced, 
while eurves are seen in the plates of fig. d, and tbe nucleus has 
been pushed up to the wall. These figures are taken from a spe- 
cimen shut up for fourteen days in October; but in summer 
the movement is much more rapid; indeed, in one case I found 
siekle- and L-shaped figures, and others like that of fig. 20 a, after 
only nineteen hours in the dark, but this is quite exceptional. 
It is only until three (exceptionally two) days that the apostro- 
phizing effect of darkness becomes visible: recovery in diffused 
light is more rapid—from forty-eight hours' confinement within 
twenty-four hours, including the night; from fourteen days’ in 
twenty-seven hours. . 
To produce negative apostrophe, however, darkness is not 
necessary. A few days in very poor diffused light may suffice to 
throw the plates into gentle curves, while at the same time move- 
ment towards a side-wall may betray itself. The curves, whether 
positively or negatively produced, I am inclined to explain in the 
same way as the sigmoid figures, of which they seem to be the 
earliest symptoms. . 
The law that positive effects require less time than negative, 
ealled in my former memoir the “law of positive progression," 
would seem to be departed from in this instance, seeing that the 
plate which. in good diffused light can swing round in seven 
minutes, takes more than twice as long to do so in sunlight. 
This departure from the law is perhaps apparent merely : in other 
respects the law’s dictates are obeyed; for not only has it been 
shown that the turning movement is quicker in high than in 
low diffused light, but the plate is much more readily apostro- 
phized positively than negatively. In fact, we have here two 
totally distinct phenomena, viz. alteration in the plate's plane and 
apostrophe, and it has been shown that when the latter comes 
"pon the scene, the former is in abeyance. Now apostrophe 
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