126 SYSTEMATIC BOTANY. 



Oscillaioria have the cells cf the filament more closely 

 united. They form dark-green masses in water, or on wet 

 earth, and exhibit an oscillating movement of the fila- 

 ments. The Nostocs, Oscillatoria, with several other genera, 

 as Rivularia, Scytonema, etc., have, in addition to chloro- 

 phyll, a soluble coloring matter, called phi/cocyanine, and 

 a less soluble one, called phyeoxanthine. They are blue- 

 green, verdigris-green, brownish-green, or even purple-red, 

 and live in fresh or stagnant water, on damp ground, 

 rocks, or decaying wood. 



ZYGOSPOREiE. 



i6o. The second division, or Zygosporeae, is composed 

 y. mostly of many-celled, filamentous 

 organisms, but some of them are uni- 

 cellular, and others a flat thalloid 

 mass ; nearly all of them contain chlo- 

 rophyll, and are aquatic. They are 

 the common Algse of our ponds and 

 streams. The modes of reproduction are by (1) fission, 

 (2) non-sexual spores (swarm-spores), and (3) zygo- 

 spores. The swarm-spores (Fig. 237) are motile, naked 

 masses of protoplasm, furnished with -cilia. They escape 

 from the cell in which they are produced, and after swim- 

 ming about for a time, fuse two and two, and a spore with 

 a thick wall is the result. Very simple, yet undoubted, 

 sexual organs exist in the members of this group. The 

 difierence between the male and female organs, however, is 

 not appreciable. The result of the union of the two sexual 

 cells is the formation of a zygospore, with thick, firm 

 walls ; the process is illustrated in the Moulds (Fig. 238). 



Fig. 237, Swann-spores, 



