178 



CRYPTOGAMS 







large bladderlike float filled with air." ^ The Gulf Weed 

 (Fig. 291, C), which collects in such quantities in the so- 

 called Sargasso seas, belongs to this group. On certain 

 coasts it grows as an attached plant. Portions which have 

 been detached and carried off by currents continue to grow 

 and multiply vegetatively as they float in the quieter areas 

 of the ocean. 



429. The brownish color of the Brown Algse is due to 

 a pigment in the cells, which probably aids the chlorophyll 

 present in the work of assimilation. 



430. Reproduction. — Reproductive cells are of several 

 sorts in this group. Fiy^st and simplest are the zoospores 

 borne in Zoosporangia (Fig. 2912, A), found in most 



members of this 



group. Their his- 

 tory is like that 

 of the larger zoo- 

 spores of Ulo- 

 thrix ; that is, 

 they germinate 



292. A, zoosporangium, and B, gametangium, of Clirectiy aiter 



Ectocarpacex; C, gametes (g) aud their con- swarming" with- 

 jugation (s). — Prixgsheisi. . 



out fusion. 

 431. Secondly/. We find processes of cell fusion, not 

 unlike those already seen in the reproductive bodies 

 of Green Algae. We may select three representative 

 cases. (1) In Ectocarpus and allied plants, zoospores 

 (gametes) are produced, which are indistinguishable from 

 the zoospores intended for direct germination, except that 

 the bodies now in mind arise in sporangia of a different 

 character (Fig. 292, B). They may conjugate in pairs (C), 

 like the small zoospores of Ulothrix. (2) In some forms 

 (Cutleria), the fusing zoospores (gametes) differ in size. 

 The larger come to rest before fusion. This is a step 

 intermediate between the condition in Ectocarpus and that 

 next to be described. (3) In the common Rockweed of 

 the shores, the gametes are egg cells and antherozoids 



1 Strasburger, "Text Book of Botany," p. 330. 



