A STUDY OF PLASTIDS AND MITOCHONDRIA 
229 
appearing in groups; figure 11, plate II, shows a peripheral cell from a 
young disc containing the two sorts of bodies of the second class. 
Returning to figure 7, as one proceeds from the periphery^ of the young 
disc toward its center, the bodies of the second class appear, on the whole, 
smaller. There seems to be a gradual decrease in their size correlated with 
an increase in their number, up to a depth of about two cell layers below 
the areolae. Here, bodies of this class begin to decrease in number, indi- 
cating a diminution in the amount of oil in the cells, while bodies containing 
from one to several starch grains begin to be seen: figures 8 and 9. 
This seriation, suggesting that at least some of the bodies are plastids, 
is better shown in figiirc/S 13 and 14, taken together, which were drawn 
from a somewhat older disc than that from which figure 7 was taken. 
Figure 14 shows two cells from still deeper within the disc, as compared with 
figure 13, from a central lenticular area in which all the cells are of this 
type and packed with storage starch. These plastids, for such they appear 
to be, are stuffed with starch and now appear merely as enveloping films, 
enclosing and separating the starch grains. The character of these starch 
grains, which show a definite hilum when stained in certain ways, as well as 
their general appearance and distribution, would indicate that they are, as 
already suggested, storage starch and that the grains are very likely strati- 
fied. It was also found on staining such a section as that shown in figure 12 
with iodine, that the starch reaction was given by all. the bodies of this 
character, even to some of the smaller ones in the peripheral layer of the 
disc. Figure 15 represents a series of stages in outline as they are seen in 
the development of starch in this disc. 
In the chloroplasts of the thallus, starch is also present in large quan- 
tities, and toward the interior of the thallus there is a region in which the 
cells are moderately full of swollen plastids, each containing a number of 
plump starch grains, not at all lenticular in appearance as they are so often 
figured. Lenticular-shaped starch grains are found, however, in the chloro- 
plasts of cells at and near the periphery, especially in the vicinity of the 
growing point of the thallus. In the cells of the disc which contain starch, 
as well as in those of the thallus, the smaller, more plastic, and darker- 
staining bodies are still seen, arranged around the periphery. The largest 
of these should be the young chloroplasts. 
In the apical cell of the thallus and in its immediate vicinity, bodies may 
be seen which I take to be the same as those already described from the 
peripheral cells of the young disc, though they are much smaller in size. 
In this region, also, and especially in the filamentous growths therefrom, 
mitochondria of various shapes appear, very much as described by Mottier 
('18) for Marchantia. 
Discussion 
It was at one time the accepted belief among botanists that chloroplasts 
arise de novo in the cytoplasm. This is definitely stated to be the case by 
