MIDLAND NATURALIST. 93 
condition of environment not unlike that when this plant is re- 
producing in July, and with the same results. Nets were produce 
in all stages and sizes during the rest of the winter and only dis- 
appeared late in Spring. In another window and in another room 
similar results were obtained with the accompanyment of zoospore 
formation. These zoospores were found in vast numbers escaping 
through a small opening in the mother cell wall. Specimens of 
the net in various stages of formation were sent to a student in 
another university, who induced zoospore formation in the cells by 
sudden lowering of the temperature and subsequently raising it. 
Such results seem to me worthy of note as I had never before had 
occasion to have growing Hydrodictyon during the winter months. 
To illustrate the regularity with which some algae will reap- 
pear in the jars even after all trace of them has been lost, Rivularia 
may be quoted as an example. Four years ago a good crop of this 
plant appeared in great abundance in one of the jars early in 
Spring. It has reappeared every year since then about the same 
time.  Zolypothrix has also come out annually in one of the jars 
the contents of which were not disturbed during several years. 
Monoecious forms of CEdogonium appear annually and usually 
early in spring. The first appearance of this plant is usually ac- 
companied with the formation of asexual zoospores which seem to 
multiply the individual filaments. This stage is usually recognized 
by the kinky twisted appearance of the plant. The zoospores 
either escape from small holes formed about the middle of the fila- 
ments, or by breaking up the cells usually near one end of each cell 
in the chain thus causing a zigzag appearance of the filament seen 
under the microscope, and a kinky interwoven appearance as they 
can be seen by the naked eye near the surface of the water. Later 
on as the filaments increase in number, oogonia and antheridia are 
formed. 
oleochaete scutata is ordinarily considered as a comparatively 
rare plant. Its periodical appearance in undisturbed aquaria is 
worthy of note. 'The plant remains attached to the walls of the 
aquaria for many months at a time, constantly increasing in diame- 
ter, often while the interior cells near the centre have completely 
rotted away, so that the plant looks like a ring rather than a plate. 
Such old plants in thelaboratory nearly always eventually illustrate 
a peculiar method of vegetative multiplication. At the edge or near 
the last ring of cells, there are developed at intervals new centres of 
