THE GEEAT GKOUPS OF ALG^E 
259 
and reddish-brown) making them very attractive. They 
show the greatest variety of forms, branching filaments, 
ribbons, and filmy plates prevailing, sometimes branching 
very profusely and delicately, and resembling mosses of 
fine texture (Figs. 222, 223, 224:, 225, 226). The differen- 
tiation of the thallus into root and stem and leaf-like struc- 
tures is also common, as in the Brown Algae. 
174. Reproduction. Eed Algae are very peculiar in both 
their asexual and sexual reproduction. A sporangium pro- 
duces just four asexual spores, but they have no cilia and 
no power of motion. They 
can not be called zoospores, 
therefore, and as each spo- 
FIG. 227. A red alga ( Callithamniori), show- 
ing sporangium (A), and the tetraspores 
discharged (). After THURET. 
FIG. 228. A red alga (Nemaliori) ; A, 
sexual branches, showing antheri- 
dia (a), oogonium (0) with its trich- 
ogyne (t), to which are attached two 
spermatia (s) ; B, beginning of a 
cystocarp (o), the trichogyne (t) still 
showing ; O, an almost mature cys- 
tocarp (0), with the disorganizing 
trichogyne (t). After KNY. 
rangium always produces just 
four, they have been called 
tetraspores (Fig. 227). 
Eed Algae are also heterog- 
amous, but the sexual process has been so much and so 
variously modified that it is very poorly understood. The 
antheridia (Fig. 228, A, a) develop sperms which, like the 
tetraspores, have no cilia and no power of motion. To dis- 
