Igt2] GRIGGS—RHODOCH YTRIUM I4I 
this starch is of course the photosynthetic activity of the host, 
but it is hardly necessary to state that the starch grains of Rho- 
dochytrium are quite different in form from those of the adjacent 
host cells. 
As would be expected, starch is most abundant and_ best 
developed in the mature resting spores, in which it forms the bulk 
of the reserve food, but it may be present at any stage in the life 
cycle. In the zoosporangia it is nearly always present toward the 
end of the vegetative period, but there is a decided tendency to 
consume it during the period of nuclear division. A marked dif- 
ference was noted in respect to starch content between zoosporangia 
gathered in 1910 and those gathered in 1908. In the former both 
“ zoospores and very young sporangia contain numerous starch 
grains, but in the latter starch appears tardily and almost always 
disappears before segmentation, leaving the cytoplasm clear and 
granular, without inclusions of any sort. 
The grains seldom exceed to in diameter and are commonly 
somewhat smaller. They are usually spherical or somewhat 
elongated, but very long or double grains are not rare (fig. 9). 
The larger grains when mounted in balsam frequently show con- 
spicuous cracks at the hilum, as is not unusual in starch grains 
generally. No definite alternating concentric layers of different 
refractive indices such as characterize many starch grains could 
be made out, but in certain grains faint concentric striae appeared 
tobe present. When subjected to the action of strong chromic acid, 
they show during dissolution the radial structure characteristic 
of starch grains in general. 
_ STARCH GRAINS UNDER POLARIZED LIGHT.—In the dark field 
obtained by crossing Nicol prisms, the starch grains show the usual 
luminous body crossed by dark bars in the two planes of polarization 
(fig. 10). But there is considerable variation in the behavior of 
different grains, both in those of the same cyst and in different 
cysts taken as a whole. Almost all conditions, however, may 
usually be found in a single cyst. Many of the spherical grains 
show no change other than the revolution of the crosses when the 
prisms are rotated, demonstrating in these grains a perfectly 
symmetrical structure, with the hilum occupying a point in the 
