21 I 
Species of Olpidiopsis , (Cornu) Fischer. 
Cornu discovered in three of the species an apparently new and 
interesting type of resting spore, the large spiny cell being accompanied by 
a smaller smooth, or slightly echinulate, one which he designated as the 
4 cellule adjacente’, as previously mentioned. In the diagnosis of O. Sapro - 
legniae , (A. Br.) Cornu, he specifically states that the presence of an adjacent 
cell is a distinguishing character of that species. He comments upon the 
fact that, inasmuch as resting spores were not seen by A. Braun, it is impos- 
sible to determine the species described by him, but wishing to preserve 
Braun’s specific name, Cornu used it for his species found on Saprolegnia. 
Cornu attributed to this new type of resting spore a sexual character. 
He considered the large cell an oogonium, and the small one an antheridium. 
Reinsch (21), some years later, observed a species of Olpidiopsis in the 
ends of swollen hyphae of a species of Saprolegnia. He described three 
types of cells occurring in the same filament. He observed the spiny rest- 
ing spores with which were associated smaller spherical cells that eventually 
discharged their contents into the larger. Changes in the protoplasm of the 
cells were noted, and the actual transfer of the male protoplasm was observed. 
He states that Pringsheim’s assumption as to the sexual nature of the spores 
is correct, but makes no reference to Cornu’s work, which, apparently, he had 
not seen. 
In 1883 Zopf (26) described an interesting species of Olpidiopsis 
parasitic in Spirogyra , which he named O. Schenkiana. This species is of 
particular interest in that it shares the peculiarity with one other species of 
the genus of possessing uniciliate zoospores. 
It was observed that the sexual plant arose as a single mass of proto- 
plasm which later put out an evagination to form the companion cell. At 
the time of fertilization no pore between the two was detected, and Zopf 
suggested that a diffusion of the male protoplasm through the wall itself 
took place. At any rate, the antheridium was completely emptied. Zopf 
had no doubt of the sexual nature of this spore. 
The following year, Fisch (10) published an account of a new form, for 
which he erected the genus Pleocystidium and named it P. parasiticum. The 
species resembles very much O. Schenkiana , and was likewise found para- 
sitic on Spirogyra. One important difference exists in the manner in which 
the sexual spores are produced. In P. parasiticum they arise, according to 
Fisch, from two or more closely associated masses of protoplasm represent- 
ing separate individuals. One of these becomes what he terms the central 
cell, and the others the companion cells, or antheridia. Fisch was not 
certain whether the cellulose membrane eventually formed about the spheres 
was developed around each individual separately or around all as a whole. 
He was inclined to the latter view. The actual passage of the protoplasm 
from the antheridium into the oogonium was observed. 
The investigations of A. Fischer (11) contain a very careful description 
