CHLOROPHYCEAE 
193 
spores or dwarf males in the life-history. A species with dwarf 
males is shown in Figure 44. 
In studying Oedogonium diplandrum, Klebs found that a change 
from a lower to a higher temperature would 
induce the production of zoospores. A culture 
which had been kept in a cold room with a 
temperature varying from 6° to 0° C., when 
brought into a warmer room with a tempera¬ 
ture varying from 12° to 16° C., produced an 
abundance of zoospores within 2 days. Light 
does not seem to have any influence upon the 
formation of zoospores in this species, but 
light is necessary for the formation of anther- 
idia and oogonia. 
We have secured an abundance of oogonia 
and antheridia by keeping the material for 4 
or 5 days in a very weak Knopf’s solution 
and then tranferring to distilled water. The 
oogonia appeared in 3 or 4 days. The method 
seems to succeed with some species, especially 
those which occur floating or suspended in the 
water, but we have not succeeded with species 
which form a fuzzy covering on grasses and 
twigs under water. Sterile material some¬ 
times fruits when brought into the laboratory 
and placed in open jars with plenty of water 
and not too much light. 
Coleochaete. — Coleochaete is epiphytic upon 
the stems and leaves of submerged plants. 
C. scutata, which is the most common species, 
has a flat, orbicular thallus generally less than 
1 mm. in diameter. C. pulvinata has a hemi¬ 
spherical thallus and might be mistaken for 
Rivularia, unless examined with a lens. 
For most purposes it is better to mount 
the whole plant, in situ on the leaf upon which 
it is growing. If it is growing on stems or 
petioles, strip off the epidermis and mount small pieces. In this way 
you get the very young stages, from the fertilized egg up to the adult 
Fig. 44. — Oedogonium: 
an undescribed species col¬ 
lected by Dr. Elda Walker. 
In A, on the left, is a dwarf 
male still showing the cap cell; 
on the right, the cap cell has 
come off and the antheridium 
at the top has discharged one 
of the sperms, but the other, s, 
still remains; in the anther¬ 
idium below are two young 
sperms. B, upper part of a 
cell, showing the cellulose ring 
which will form the side wall 
of the new cell. The nucleus 
is in the spirem stage of 
division. X 280. 
