172 



CBYPTOGAMS 



Sphere. Its only known mode of reproduction is by 

 division. That is, eacli individual divides by a cross 

 wall, and the two new individuals so produced increase in 

 size. Before they separate they may each again divide ; 

 and ill fact the plants are commonly found cohering in 

 small colonies (Fig. 284, B). 



416. Ulothrix. — The fine unbranched filaments of Ulo- 

 thrix are abundant in fresh water, wdiere they grow 

 attached to stones, sticks, etc. (Fig. 285, a). The fila- 

 ments increase in length by the division and elongation of 

 any or all of the cells. When Ulothrix is about to repro- 

 duce, its cells divide internally, so that within 

 each one are produced several cells ; but the 

 latter liave )io cell wall formed about them. 

 When these naked cells escape, by the rupture 

 ¥0,^ of the mother cell waW, it is seen that they are 



2S5. Ulothrix: o, a young filament: b, larger zoospore; c. escape of these 

 spi>res; J, e, escape and conjugatiou of smaller zoospores. — Dodf.l-Pukt. 



provided with hairlike organs called cilia, by means of 

 which they swim energetically about (Fig. 28.5, /), (7). 

 The motile cells Tcalled, from their animal-like power 

 of locomotion, zooqjores) are of two kinds, large and 

 sm:ill. The larger have four cilia (Fig. 285, h). After 

 a short active period they settle down, lose their cilia, 

 invest themselves with cell walls, and germinate In' 

 growing out into new filaiuents. The smaller zoospores 

 are provided M'ith but two cilia. After swarming they 

 fuse (Fig. 285, c), generall}' in pairs. This process, 

 wherein two cells unite to form the germ of a new plant, 

 is called coiijufii'ition. The body formed Ijy tlie conjuga- 

 tion of two similitr cells is a zi/i/osjiore. In tlie case of 



