144 BOTANICAL GAZETTE [FEBRUARY 
The development of the zoosporangia 
As already stated, the zoosporangia are distinct from the 
resting spores from the very beginning. The youngest stages 
seen were approximately as large as the youngest resting cysts, 
namely, 60-80 in length. These future zoosporangia do not 
form external buttons, and the neck, even at the very first, is of 
comparatively large diameter (fig. 12). While still very young, 
the cyst begins to swell out from the initial tubular form, and soon 
assumes the roughly turbinate shape characteristic of the mature 
zoosporangium. But before the parasite begins to expand, it 
generally penetrates straight into the tissues until it has reached 
the vicinity of a vascular bundle. The final size of the cyst is_ 
roughly proportional to the length attained by the germ tube, but 
of course the relation is somewhat accidental, since it is the stronger 
bundles capable of supplying more abundant food which are the 
more deeply buried. In the leaves the distance is approximately 
100 #,, while in the stems, where the vascular bundles are relatively 
deeply buried beneath the cortex, a length of 300 or more is 
frequently attained (fig. 14). It thus happens that size is no 
criterion of the age of a cyst, some uninucleate cysts being much 
larger than some which are far along in division, as shown by 
figs. 12 and 26, which are drawn to the same scale. 
Sometimes, while still in the tubular condition and usually before. 
full size has been reached, a characteristic plug is formed at the 
mouth of the zoosporangium. In all but the youngest stages this 
is the most convenient character for distinguishing the zoosporangia 
from the resting spores, since the latter never develop a plug. 
But the plug is subject to great variations in size, and in rare 
instances may never develop at all. The most typical form is a 
solid top-shaped mass which stains deeply and uniformly through- 
out (figs. 14, 15, etc.). Often it is a hollow, bell-shaped structure 
(fig. 21), as figured by LAGERHEm™ (see above, p. 136). In some 
instances such bell-shaped plugs were found to be perforated so as 
to place the interior of the cyst in open communication with the 
outside. Some solid plugs were observed which stained lightly, 
except on the lateral edges (fig. 24), giving the appearance of bell- 
shaped plugs which had been later filled up. In many cases the 
