370 MR. S. LE M. MOORE’S STUDIES 
under the most favourable conditions requires at least half an 
hour for its completion; and there is reason to believe that the 
swinging movements in sunlight are associated with apostrophic 
ones. Ought it therefore to be a matter for wonder that these 
movements are performed in periods intermediate between those 
required for the turning of the plate under the most favourable 
circumstances in diffused light and those necessary for the pro- 
duction of apostrophe ? 
Of light as a fructifying cause, Mesocarpus affords an interesting 
example. This is shown in two ways: if a specimen be so 
arranged that, the plate having been in full face, considerable 
approaches are making towards the profile position, or vice versá, 
on plunging now into darkness and examining after a short 
interval, the movement will be found to have been almost or 
entirely completed. A second instance is yielded by the behaviour 
of the plate in darkness. I find that correct prediction as to 
the position (face or edge up) which any given plate will occupy 
after a few hours’ withdrawal of light is impossible; for in some 
of the cells the plates which previously lay face up will now show 
their edge, and vice versd ; indeed, difference is frequently observed 
even in neighbouring cells. These variations I venture to explain 
on the view that a registration of the impulses of light goes on 
in the chloroplast, so many urging the plate into one plane and 
so many into the other. Should the two sets of impulses be 
equal, then no swinging movement ensues; but if one set predo- 
minate, the plate turns accordingly. 
It is submitted, then, that— 
(1) In diffused light the chlorophyll plate of Mesocarpus sets 
itself so as to cut the greatest number of light-rays of the highest 
intensity. The time occupied by the turping movement varies 
inversely as the strength of the illumination. 
(2) In weak sunlight the plate turns edge up; but the effect 
of strong insolation is to drive it into apostrophe: when different 
sides of the cell are approached by different parts of the plate, 
then sigmoid and saddle-shaped figures result. 
(8) The plate can be negatively apostrophized, but only after 
the lapse of a period much longer than is necessary for positive 
apostrophe to declare itself; the negative movement comes 0 
in low light as well as in darkness. 
(4) When the turning movement is in progress, it will not be 
