IN VEGETABLE BIOLOGY. 243 
among others, will show. An Elodea-plant was placed in a moist 
bag, its tip only protruding. The bag having been fixed to a 
cardboard frame, one of the leaves at the tip was spread out in 
water on a small glass stage fixed in a hole in the cardboard, and 
covered with a thin cover-slip. The leaf was then arranged on the 
microscope-stage so as to be illuminated by the mirror; and in 
half an hour rotation had set in. At 2.30, fifty minutes after 
beginning the experiment, the bag and its contents were removed 
to the dark; and at 6 o’clock that evening the protoplasm was 
slowly rotating. At 8.40 next morning there was still faint rota- 
tion near the apex of the leaf; but by 12.45 on the day after 
complete quiescence had supervened. A still more satisfactory 
observation—in that temperatures were carefully noted—is the 
following. An Elodea-plant was placed in a shallow vessel nearly 
filled with water, set on the sill of a window facing north. At 
midday the protoplasm was in slow rotation, the temperature of 
the water being 57° F.; and the vessel was now set in darkness 
in a south-facing room. Examined at 8.40 r.m., the tempera- 
ture of the water being now 68° F., rotation had stopped, and the 
grains were in epistrophe. Next morning the vessel was replaced 
on the north side of the house, and, rotation having been induced, 
removal to darkness was effected at 2.80 p.m.; at 6.15 the same 
evening rotation had ceased except in one cell of the midrib, in 
which it was very faint—temperature in both light and darkness 
65° F. 
It is unnecessary to dwell more upon this point ; but some in- 
vestigations, of which Vallisneria was the subject, may here be 
detailed. A young Vallisneria-plant which had been kept for 
several days in a vessel placed in low light, and showed no 
trace of rotation, was removed on a dull August day to a small 
glass jar containing water, in which it was totally immersed, 
and brought up to poor diffused light, undergoing less than 1? 
variation of temperature by the process. When observed two 
and a half hours afterwards, rotation was found to have been set 
up in the large internal cells*. The jar was now (3.15 P.M.) 
removed to the dark chamber, and rotation was ascertained to be 
in progress throughout the following day ; but at 5 o'clock in the 
* This was observed by focussing through the superficial tissue—not a dif- 
ficult task by any means. The grains were carried along in the protoplasmic 
stream just. as happens upon sectioning. 
