DIV. I 



THALLOPHYTA 



405 



FTQ. 341. A, B, Oedogonium. : A, escaping swarm-spores ; B, free 

 swarm-spore. C, D, Oedogonium dliatum : C, before fertilisa- 

 tion ; D, in process of fertilisation ; o, oogonia ; a, dwarf 

 males ; S, spermatozoid. (x 350. After PRINGSHEIM. ) 



FIG. 342. Bulbochaete inter- 

 media. A, Oospore. B, 

 Formation of four swarm- 

 spores in the germinating 

 oospore. (x 250. After 

 PRINGSHEIM.) 



ranea (Fig. 345) will serve as an example of such calcareous Algae. The thin stalk 

 of the thallus is attached by 

 means of rhizoids, while the 

 umbrella-like disc consists of 

 closely united tubular out- 

 growths, each of which is to 

 be regarded as a gametangium. 

 The contents of the latter do 

 not form the biciliate gametes 

 directly, but first divide into 

 a large number of firm-walled 

 cysts. These remain in the 

 resting condition throughout 

 the winter, and then give rise 

 to numerous gametes which 

 conjugate in pairs. Thezygotes 

 germinate promptly and grow 

 into new plants. 



Order 5. Siphonales 



The Siphoneae are distin- 

 guished from the preceding 

 groups of Algae by the struc- 

 ture of their thallus, which, 

 although more or less profusely 

 branched, is not at first divided 

 by transverse septa. The cell 

 wall thus encloses a continu- 

 ous protoplasmic body in which FlG - 343. Coleochaete pulrinata. 1, Antheridium (a) and 

 numerous nuclei and small >' oun g nium (>- *. Oogonium shortly before open 

 ,, , . ing. 3, Fertilised oogonium ; ek, nucleus of the ovum ; 



green chloroplasts are em- sk> male nucleugi ^ Oospore enclosed to form the 



bedded. The same type of fructification." 5, Germinating oospore. (After 

 thallus is also met with in OLTMANSS.) 



