172 



CRYPTOGAMS 



sphere. Its only known mode of reproduction is by 

 division. That is, eacii 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 in 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, where they grow 

 attached to stones, sticks, etc. (Fig. 285, <x). 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 tlie 

 latter have no cell wall formed about them. 

 When these naked cells escape, by the rupture 

 of the mother cell wall, it is seen that they are 



285. Ulothrix: a, a young filament; 6, larger zoospore; c, escape of these 

 spores ; d, e, escape and conjugation of smaller zoospores. — Dodkl-Port. 



provided with hairlike organs called cilia, by means of 

 which they swim energetically about (Fig. 285, b, d). 

 The motile cells (called, from their animal-like power 

 of locomotion, zoospores^ are of two kinds, large and 

 small. The larger have four cilia (Fig. 285, b). After 

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

 invest themselves with cell walls, and germinate by 

 growing out into new filaments. The smaller zoospores 

 are provided with but two cilia. After swarming they 

 fuse (Fig. 285, e), generally in pairs. This process, 

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

 is called conjugation. The body formed by the conjuga- 

 tion of two similar cells is a zygospore. In the case of 



