INTRODUCTION 25 



represented by the air-bladders which secure 

 buoyancy for the Fucaccce and Laminariacece, while the 

 whole interior of many other forms is hollow. The 

 mucilaginous character of the cortical tissue of 

 many Algae protects the internal cells from drying 

 while exposed between tides. In the rind of the 

 Laininariacece there are special gum -passages, while 

 in Splachnidium and other forms the whole of the 

 interior is filled with a mucilaginous substance. 

 Adhesion to the substratum is effected by sucker- 

 like haptera, by basal layers of cells, or by rhizoid 

 filaments which penetrate the substratum. 



A comparative review of the reproductive pro- 

 cesses of seaweeds would be unprofitable by itself, 

 since such a treatment would lack symmetry without 

 reckoning in the fresh-water forms. It would be, 

 moreover, appropriate only in a treatise on the 

 general morphology of all Algae. Details of such 

 processes are given in the accounts of the differ- 

 ent groups, but it is of interest to note now 

 the occurrence in seaweeds of isogamous and ooga- 

 mous forms of reproduction, and the propagation 

 by spores and other bodies of purely vegetative 

 character. Though these modes of reproduction are 

 represented in their typical forms among seaweeds, 

 certain subordinate types are confined to the fresh- 

 water Algae. Conjugation by non-ciliated gametes, 

 for example, occurs in the sea only among the 

 Diatomacecc, since the Gonj-ugatce, of which it is 

 characteristic, are all fresh- water Algae. There 

 appears to be an almost equal amount of diversity of 

 type of reproduction among fresh-water and marine 



