TYPES OF CRYPTOGAMS; THALLOPHYTES 217 
process may be studied by daylight. In such ways the series of phe- 
nomena shown in Fig. 152 has been 
accurately followed. If the stu- 
dent cannot follow these operations 
under the microscope, he may, at 
least, by looking over the yellower 
portions of a mass of Spirogyra, find 
threads containing fully formed 
zygospores, like those shown in 
B, Fig. 152. 
Fic. 152. Conjugation of Cells of Green Algee. (Much magnified.) 
I, Conjugation of Desmids. A, a single plant in its ordinary condition; 
B, empty cell-wall of another individual; C’, conjugation of two indi- 
viduals to form a spore by union of their cell-contents. 
II, Conjugation of Spirogyra. A, two filaments of Spirogyra side by side, 
with the contents of adjacent cells uniting to form spores, z. At the 
bottom of the figure the process is shown as beginning, at the top as 
completed, and the cells of one filament emptied; B, a single filament 
of another kind of Spirogyra, containing two spores, one lettered z. 
(4 magnified 240 diameters; B, 150 diameters.) 
THE STUDY OF PLEUROCOCCUS 
274. Occurrence. — Pleurococcus may be found on old fences, roofs, 
and many similar places, particularly on the bark of the north side 
of trees. The individual plants cannot be detected by the naked 
eye, but when grouped in masses they form a powdery green covering 
over indefinite areas of bark. Plenty are seen where it is moist. 
