THE ALG 223 
another cell in a reproductive process is called a gamete. 
If the gametes are similar, the resulting spore is called a 
zygospore. In the case of Spirogyra the zygospores are of 
service to the species by tiding over the winter season, or, 
in regions with a long, rainless summer, the dry season. 
In cool climates they are formed during the summer, but 
usually sink and remain long dormant, each throwing out 
a new filament and forming a new colony in the spring. 
283. Summary of the Conjugating Alge.— These alge 
all occur in fresh or merely brackish water. Every cell has 
a nucleus. The chlorophyll is arranged in comparatively 
large protoplasmic bodies, which often take the form of 
spiral bands. The manner in which the zygospores are 
formed from the union of non-motile cells in Spirogyra is 
characteristic of the conjugating alge. 
One family, that of the desmids (Fig. 154), is in some 
respects similar to the preceding class (the diatoms, Fig. 
158). Sprogyra and some other thread-like genera of the 
conjugating algze much resemble the next class (the green 
algee), though not the one shown in Fig. 157. 
(DOGONIUM, ONE OF THE GREEN ALG 
284. Occurrence. — Edogonium is found in pools, quiet 
ponds, horse-troughs, or slow streams of water throughout 
the year. This filamentous alga grows attached to stones, 
dead leaves, or other submerged objects. 
285. Gross Structure.1— Examine with the magnifying glass a 
small amount of the material in a little water, and note: 
(a) Whether the filaments are simple or branched. 
(b) Whether they are long or short. 
(c) Differences between the base and tip. 
1 See Bergen and Davis’ Principles of Botany, Sect. 220. 
