1912} GRIGGS—RHODOCHYTRIUM 145 
plug is secondarily surrounded by several concentric layers of 
material, evidently laid down at intervals. Such plugs show great 
variation in appearance (figs. 17-20), presumably on account of 
variations in the conditions of deposition. 
As in the resting spore, the protoplast is at first highly vacuolate, 
consisting of a peripheral layer of cytoplasm connected with the 
central mass about the nucleus by radiating strands. As growth 
proceeds, the cytoplasm becomes more abundant in proportion to 
the vacuoles, but the zoosporangia always have larger vacuoles 
than the resting spores. Sporangia of different ages, however, 
vary considerably in this regard. The larger cysts usually have 
larger vacuoles than the smaller. In later stages there is always 
one large vacuole which occupies the upper half of the cyst, the 
protoplasmic contents, except for a thin peripheral layer, being 
confined to the basal portion, as shown in the figures. The numer- 
ous rhizoids which are put out from the base are like those of the 
resting spore. 
The cysts reach full size before there is any indication of division. 
But when division commences, the binucleate, tetranucleate, and 
later stages follow each other in rapid succession (figs. 22-28), 
until a large but variable number of nuclei have been formed. 
Upon completion of the period of nuclear division, segmentation 
occurs and zoospores are produced. The coenocytic cysts are 
comparatively rare. Never, even in the most favorable material, 
do they approach in abundance the primary cysts or those in which 
segmentation is complete. 
The shape of the cysts seems to be determined largely by acci- 
dental variations in the compactness of the tissues in which they 
lie. The penetrating germ tubes follow to a large extent the path 
of least resistance. This sometimes leads them to spread out in 
the tissues (fig. 2), and causes considerable epee in the form 
of the mature cyst. 
In those cysts which have abundant ak. clear spaces, roughly 
corresponding in size and shape with the primary nuclei, persist 
for some time after division (figs. 22, 57). Similar appearances 
are found sometimes in the telophases of the later mitoses (fig. 66). 
These are not vacuoles, as might at first appear from contrast 
