210 MR. 8. LE M. MOORE’S STUDIES 
lation. By exposure to darkness for a few days, the grains of 
either of the two rows of palisade-cells of Eschscholtzia californica 
seedlings will be found massed together so closely that, as in 
the mesophyll under similar circumstances, the masses appear, but 
for their colour, as local thickenings of the wall. Fig.8 (Pl. VII.) 
represents in a bird’s-eye view two palisade-cells with massed 
grains; and figs. 9a and 4, which are sectional views, show that 
the masses are collected in the narrowest parts of the cell, that 
is to say in fore-and-aft fashion. The difference between darkling 
and illuminated palisade-tissue is easily made out, since in the 
latter the grains are disposed uniformly round the circumference 
in bird’s-eye view, whereas in the former this is not the case. 
Whether or no the palisade-tissue of other types shows the same 
peculiarity has not yet been determined. 
If a plant with negatively apostrophized chlorophyll be removed 
to diffused daylight, the grains move into epistrophe after a 
period depending on the quality of the light and on the type 
used. Thus, three weeks’ apostrophizing of Elodea was repaired 
by four days in diffused light; five hours’ of Stellaria media meso- 
phyll by three and a half hours; ten days’ of Oxalis Acetosella by 
three days, and so on. These and similar cases are treated of 
under a subsequent head. (See the table on p. 234.) 
Recovery from massed negative apostrophe is possible, provided 
that, in order to induce it, there be no necessity to keep a plant 
too long in darkness. As with massed positive apostrophe, so 
with negative; a longer time is needed to epistrophize the grains 
than if they started from simple apostrophe. But it may happen 
that, in order to cause massing, so long an exposure to the dark 
is essential, that recovery of the cell to its normal condition is 
impossible. I have seen this in the marginal cells of Lemna tri- 
sulca, with the exception of a few near the base, in which recovery 
took place. It must, however, be mentioned that L. trisulca is 
soon weakened by confinement in a close room, even under favour- 
able conditions of illumination; it is therefore possible that the 
failure to recover is not entirely due to withdrawal of light. 
A still further change in the disposition of chlorophyll some- 
times results from prolonged withdrawal of light. Thus the cells 
of Funaria hygrometrica plants, set in the dark for three weeks, 
were found to be of one of the following descriptions :— 
(i.) Quite dead and empty, except for a few spherical colour- 
less parte. 
