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 Sjpirogyra 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 Algae. — These algse 

 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 algse. 



One family, that of the desmids (Fig. 154), is in some 

 respects similar to the preceding class (the diatoms, Fig. 

 153). Spirogyra and some other thread-like genera of the 

 conjugating algse much resemble the next class (the green 

 algse), though not the one shown in Fig. 157. 



(EDOGOXIUM, ONE OF THE GREEN ALGJ3 



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.^ — -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. 



(J) Whether they are long or short. 



(c) Differences between the base and tip. 



1 See Bergen and Davis' Principles of Botany, Sect. 220. 



