122 THE ESSEX NATURALIST.
in length (i.e., just under a twelve-thousandth of an inch), broadly
oval, with a highly retractile globule near the posterior end. The
single long flagellum was held behind as the zoospore moved
through the water. This type of zoospore is characteristic of the
Chytridiales. I have sometimes found specimens among the
nannoplankton when water has been centrifuged for the purpose
of obtaining these very minute forms of aquatic life. But as
such zoospores do not remain active very long it is somewhat of
an accident if they are found in this way.
As already mentioned, the free-swimming zoospores did not
move very far away; in fact, several soon settled down on the
same Chlorogonium and later two were seen on another specimen,
but none were seen at any time attached to any other species of
alga.
When a Chytrid zoospore settles down it adheres by its
anterior end, sheds or absorbs its flagellum, and succeeds in some
remarkable way in perforating the cell-wall of the host-plant.
After that there are various possibilities as to the further
development. In some cases a single or branching hyphal thread
may be formed in the interior of the host-plant and zoosporangia
may also be formed inside. In the case under consideration
the zoospore itself developed outside into a zoosporangium by
absorbing nutriment from the Chlorogonium. I am not sure
whether it always gave rise to a hyphal thread, as only in one
instance could I make out such a structure. In that case the
hypha ran in a curving path into the clear space in front of the
chloroplast. In other cases there seemed to be only a very short
tube connecting the zoosporangium with the interior of the
Chlorogonium, but in all cases where the zoosporangium was
opposite to the chloroplast there was a little bay in the latter.
The name of the Chytrid described above appears to be
Phlyctidium chlorogonii, Serbinow,9 and its occurrence in this
country is, I believe, now recorded for the first time.
EXPLANATION OF THE FIGURES AND LETTERING.
Fig. 1. Chlorogonium elongatum, var., with three zoosporangia
of the Chytrid Phlyctidium chlorogonii in different
stages of development. x 1250.
9 Scripta Botanica Horti Universitalis Imperialis Petropolitana, Vol. xxiv., 1907, p. 156,
Pl V., Figs. 11-17.