GROUP I. THALLOPHYTA : ALGM : PH^OPHYCEj;. 



255 



in other cases the peripheral cells of subterranean nodes, instead of giving rise 

 to leaves, grow out into small cellular appendages which become filled with 

 starch, and are known as starch-stars. When the plant has died down in the 

 winter, these bulbils and starch-stars persist, and, in the following spring give 

 rise to new plants. Again, instead of normal branches, the plant may pro- 

 duce branches of peculiar structure, called embryonic branches because they 

 resemble the embryo, which become separate and grow at once into new plants. 



The Characese are classified as follows : 



Fain. 1. Nitellea : corona consisting of ten 

 cells ; includes the genera Nitella, Tolypella. 



Fam. 2. Charece : corona consisting of five 

 cells ; includes the genera Chara, Lampro- 

 thainnus, Lycnothamnus, Tolypellopsis. 



The stem and leaves of the Nitellese have 

 no cortex ; those of most of the Chare ae have 

 cortex. They all inhabit fresh or brackish 

 water. 



Sub-Class III. PHJ;OPHYCEJ:, or 

 Brown Algee. The body may consist 

 of a single cell (e.g. Diatomaceae, 

 Syngeneticae), but is generally multi- 

 cellular ; it is never coenocytic. When 

 multicellular, it presents various de- 

 grees of morphological differentiation, 

 being usually differentiated into shoot 

 and root, and in some cases (e.g. 

 Cladostephus, Sargassum) into stem, 

 root, and leaf. 



Vegetative multiplication is com- 

 mon in the unicellular forms, in which 

 it is effected by division ; in a few 

 forms (e.g. Choristocarpus, species of 

 Sphacelaria) it is effected by means 

 of gemmae. 



The life-history of most of the members of this sub-class is but 

 imperfectly known. In some cases it certainly does not present 

 an alternation of generations, on account of the absence either of 

 asexual reproduction (Fucaceae) or of sexual reproduction (Syn- 

 geneticae). In other cases, again, both sexual and asexual repro- 

 duction are known (e.g. some Ectocarpacea?), but since the two 

 kinds of reproductive organs are borne on the same individual, 

 either simultaneously or at different times, no alternation of gener- 

 ations can be traced. In yet others, distinct sexual and asexual 



FIG. 183. Chara fragilis (after 

 Pringsheim: x 4). Heteroblast'c 

 embryogeny; ap apical portion of 

 shoot of the embryo ; r primary 

 root of embryo, springing from the 

 oospnre; sr adventitious roots; t 

 leaves, amongst which lies the grow- 

 ing-point of the adult shoot; t 

 intermediate cell. 



