1902] CLADOCHYTRIUM ALISMATIS 53 
some of the experiments the plants were allowed to take root in 
soil covered with water, and the leaves removed as desired for 
examination. It was found, however, that even a piece of a 
leaf would remain fresh and active in a drop of water in a Van 
Tieghem cell for several days, and thus could be watched 
directly. The best results were obtained with young seedlings 
whose roots were placed in one of the arms of a Ward cell 
partly filled with a nutrient solution, and the first grass-like leaf 
was held up by a little cotton support so that it adhered to the 
cover glass containing a drop of water and the sporangia. 
This species of Cladochytrium is placed by some botanists 
under the genus Physoderma, because it was not known to have 
a temporary sporangium. Our experiments were somewhat sur- 
prising, since they showed not only that such a stage existed, 
but that it was of a quite peculiar type. When this was first 
seen its relation to Cladochytrium was not suspected, but when 
it became evident that the two were connected, a large number 
of culture experiments were made in order to remove all doubt. 
The result was that this temporary stage appeared in every case 
where the resting sporangia germinated in water containing the 
young Alisma, and failed to appear in every case where the 
sporangia did not germinate and in the checks, both where 
nothing was placed with the young Alisma and where merely a 
piece of the old Alisma leaf which contained no sporangia was 
added. £6 
7 As the zoospores are usually quite active for some time, it 
was impossible to follow a single one from the time of its exit 
from the sporangium until it came to rest. It was not difficult, 
however, when they began to grow sluggish in their movements, 
to find them settling down on the Alisma leaf and to watch 
them in their subsequent development, so that there was no ~ 
doubt as to their identity. They almost always fix themselves 
on the epidermis just above the wall dividing two cells (figs. 7-4). 
Many do not succeed in penetrating the leaf, as the majority of a 
2 . tect an entrance. In such cases the zoospores are sooner or 
those that were continuously observed during this stage failed a 3 . 
