7 
x 
INTRODUCTION 25 
represented by the air-bladders which secure 
buoyancy for the Fucacew and Laminariacecee, while the 
whole interior of many other forms is hollow. The 
mucilaginous character of the cortical tissue of 
many Alge protects the internal cells from drying 
while exposed between tides. In the rind of the 
Laminariacee 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 Algz. 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 Algse. Conjugation by non-ciliated gametes, 
for example, occurs in the sea only among the 
Diatomacee, since the Conjugate, of which it is 
characteristic, are all fresh-water Alge. There 
appears to be an almost equal amount of diversity of 
type of reproduction among fresh-water and marine 
