THE ALG^E 



125 



warmer Atlantic, are found floating in great masses. It seems still 

 somewhat questionable whether these masses are derived from 

 originally attached plants, or whether they spend their whole 

 existence floating on the surface. 



Cell -structure. The simpler Phseophycese are composed of mostly 

 uniform cells, uniuucleate, and within their cell-membrane several 

 chrornatophores may be seen, generally small oval disks, less com- 

 monly elongated, somewhat ribbon-shaped. Rarely but a single 

 chromatophore is present. Sometimes, as in Ectocarpus, pyrenoids 

 like those of the Chlorophycese are present. 



Among the highly developed large Kelps and Fucaceae, the tissues 



FIG. 96. a, Sphacelariafilicina, top of filament; b, S. cirrhosa, showing unilocular 

 sporangia; c, the same, showing plurilocular sporangia. (After MURRAY.) 



are correspondingly well developed, assimilating, conducting, and 

 mechanical tissues being demonstrable. 



Reproduction. Much the same development of the reproductive 

 parts is seen as we have observed among the Chlorophyceae ; but on 

 the whole, notwithstanding their very highly developed vegetative 

 structures, the reproductive organs are simpler than in the Chloro- 

 phycese. Zoospores, with two laterally attached cilia, occur in many 

 of them (Fig. 99, D), but are not known in the Fucaceae, the highest 

 order. In some of the orders they are the only forms of reproduc- 

 tive cells known, this being the case in all of the giant Kelps. 



Where sexual cells are produced, they are always ejected into 

 the water when fertilization is effected. There is much the same 



