208 MR. 8. LE M. MOORE’S STUDIES 
difference in the relative position of the chlorophyll-grains in the 
lowest of the three layers; after ten days, however, apostrophe 
has decidedly set in (Pl. VII. fig. 3), but whether massing ensues 
upon further exposure to darkness is uncertain, all that can here 
be said is that after four more days it has not begun. In the 
same way, thecells immediately abutting on the lower epidermal 
layer of young autumnal leaves of Saxifraga granulata show only 
faint signs of apostrophized chlorophyll after a week's confinement 
in the dark, and even after three weeks apostrophe is very 
incomplete ; and although it seems to be entirely brought about 
in the mesophyll of Pteris cretica kept in the dark for four weeks, 
yet even this long period is insufficient for Pteris serrulata. 
This is much the same state of things that earlier observers have . 
found to occur in prothallia &c. and in Elodea and Vallisneria. 
Frank's statement that apostrophe is not induced in the two 
last within ten weeks I can well believe, my own darkling plants 
showing only partially apostrophized chlorophyll after six weeks’ 
withholding of light, by which time they were so debilitated that 
it was thought unnecessary to continue the experiment. More- 
over, negative apostrophe is very slowly brouglit about with 
Callitriche verna, uninjured parts of the leaves of which have 
their grains not quite all in apostrophe after three weeks' darkness; 
and in Lemna trisulca, although apparently somewhat different 
from other aquatic plants, in that apostrophe is nearly perfect in 
its cells within a few hours, yet in all my experiments a few of the 
grains in the marginal cells remained in epistrophe and had not 
all moved on to the side-walls even after three weeks. The 
grains of a debilitated specimen of Utricularia vulgaris, the only 
one available, had not all of them passed on to the side-walls 
after two days in the dark: those of Ceratophyllum demersum 
likewise move very slowly into negative apostrophe; indeed, I 
have seen darkling plants of this species showing scarcely any 
sign of a fortnight's incarceration. 
And as in shade-loving Cryptogams, like fern-prothallia and 
most Musci and Hepatice, negative epistrophe is very slowly 
induced, so, too, aquatic Cryptogams would seem to offer the same 
peculiarity if Hypnum fluitans be not an exception, the grains 
of the wider cells at the base of the leaves of this type not having 
been completely apostrophized after a month in darkness. 
Before leaving this subject it may be mentioned that it is not 
always necessary to withdraw light altogether in order to induce 
