250 STUDIES IN VEGETABLE BIOLOGY. 
applies, to a certain extent, to negative rotation, as movement 
can usually be traced in the internal cells a little further towards 
the leaf-base than in the external ones; and it frequently per- 
sists in the external distal cells a little Jonger than in their im- 
mediately underlying fellows. Further down the leaf the chlo- 
rophyll is in more or less perfect apostrophe; but after four 
months in the dark, I have found rotation to be in progress 
throughout the greater part of the leaf. It sometimes happens 
that massing of the grains in the cell-corners preludes rota- 
tion. Closely similar results are yielded by Elodea; but I am 
not in a position to treat of this matter in detail. 
The time requisite to induce negative rotation may be curtailed 
by any agency whereby protoplasmic tone is lowered. Thus in a 
small piece of Elodea consisting of three or four leaf-whorls 
rotation is set up weeks earlier than in intact plants. The most 
rapid way of lowering the tone is by poisoning the protoplasm. 
li is therefore not a surprising circumstance that, if an Elodea- 
plant be placed in the dark in a weak solution of ferrous sulphate, 
rotation will supervene within forty-eight hours, and will con- 
tinue until the death of the cells. 
DESCRIPTION OF PLATE VII. 
(With the exception of No. 4, the figures represent the objects seen by the aid 
of Hartnack’s No. 7 objective, ocular No. 4, giving a magnification of 450 
diameters ; but the drawings are not strictly to scale.) 
Figs. 1 & 2. Mesophyll cells of Eschscholtzia californica seedlings, seen from 
above: 1, in diffused light ; 2, after remaining in darkness overnight. 
Fig. 3. Ozalis Acetosella. Cell of mesophyll from leaf set in darkness for ten 
days, the large chlorophyll grains showing an evident tendency to 
apostrophe. 
Fig. 4. From Funaria hygrometrica. Cell of a leaf from a plant which has 
remained a fortnight in very low light, the grains coming out from 
apostrophe to collect in the proximal end of the cell. The shaded 
grains came into view on further focussing : two of them (p, p) were 
in profile. 
Figs. 5 a & b. Cells from the leaf-sheath of Poa annua twenty-two hours 
after its removal to darkness, mounted in water under a cover-slip 
meanwhile; the chlorophyll has collected to a greater or less extent 
round the nucleus. 
Figs. 6 a, b, c. Massing of chlorophyll in a small piece of an Elodea-plant 
kept in the dark about ten days: a, fore-and-aft, b, corner, and c, 
nuclear arrangement, - 
