THALLOPHYTA: AWAK 



43 



lilies and cattails. Depending on the species, the vegetative body is 

 either a branching filament, a cushion with free branches, or a circular 

 disk with radiating rows of cells (Fig. 31 A). When disk-like, it rarely 

 exceeds 5 mm. in diameter. Some of the cells bear hair-like outgrowths, 



Fig. 31. Coleochaete scutata, a discoid species. A, a small vegetative plant with numerous 

 zygotes overgrown by the surrounding cells, X150; B, a small group of vegetative cells, 

 one of which is giving rise to a zoospore, and an escaped zoospore, X500; C, vegetative cells 

 giving rise to antheridia, and an escaped sperm, X500; D, cross section of portion of thallus, 

 showing a zygote, X350. 



each with a sheath at its base. Each cell has a single nucleus and a 

 chloroplast with one or sometimes two pyrenoids. Growth is always 

 apical, in the discoid species occurring by means of a marginal meristem. 

 Biciliate zoospores, formed singly, may arise in any vegetative cell (Fig. 

 31JB). They escape through a pore in the cell wall. 



In being heterogamous, Coleochaete makes an advance over the other 

 Ulotrichales that have been considered. In the discoid species antheridia 

 are formed by the division of a vegetative cell into smaller cells, the 



