240 PART IV. CLASSIFICATION. 



of the body being merismatic (e.g. Spirogyra, Ulothrix, Ulva). In 

 some few cases (e.g. Volvocoideae, Botrydium) there is no growth 

 after the embryo-stage. 



The primary root is never developed in due proportion to the 

 shoot ; consequently, in order to ensure the attachment of the 

 plant, adventitious roots are very commonly formed on the shoot, 

 and when the shoot is dorsiventral unicellular root-hairs are 

 commonly developed on the surface in contact with the substratum. 

 In some cases special organs of attachment (haptera, see p. 48), 

 are developed on the shoot ; they may be adhesive discs borne on 

 on the ends of branches of the shoot (e.g. Plocamium coccineum), 

 or root-like out-growths as in Laminaria bulbosa, where at the 

 base of the shoot, a large umbrella-shaped out-growth is formed, 

 bearing numerous haptera on its upper and outer surface. 



The leaves vary in form. In a few cases they somewhat 

 resemble the foliage-leaves of the higher plants : in others (e.g. 

 Cladostephus, Chara) they resemble the stem and its branches, 

 but are distinguished by their limited growth ; in others again 

 (e.g. Polysiphonia and other Rhodophyceae), they are filamentous 

 and hair-like. 



The Reproduction of the Algae is effected in various ways. 

 Vegetative multiplication takes place in the unicellular forms 

 (e.g. Cyanophyceae, Protococcoideae, Desmidieae, etc.) by cell-division, 

 in some of the higher forms (e.g. Sphacelaria, Chara, Melobesia) by 

 means of multicellular gemmae (see p. 49). Non-motile cells, with 

 a cell- wall, which are probably gemmae, are thrown off by Vaucheria 

 gcminata, and sometimes by other species of Vaucheria (Chloro- 

 phyceae). Reproduction by means of asexually-produced spores 

 occurs with but few exceptions (e.g. Conjugatse, Fucaceae, Characeae). 

 Sexual reproduction is general throughout the class, though it has 

 not yet been observed in all forms ; it appears to be definitely 

 absent in the Cyanophyceae, and in some of the lower Chlorophyceae 

 (e.g. some unicellular Protococcoideae). 



There are various modes of sexual reproduction in the group. 

 The following is an enumeration of them (see also p. 58) : 



I. Isoyamy : the sexual cells are similar gametes ; process, 

 conjugation ; product, a zygospore. 



(a) Gametes ciliated (planogametes) ; set free ; e.g. Ulothrix, 

 Pandorina, Ectocarpus, Cutleria. 



(6) Gametes not ciliated (aplanogametes) ; not set free in the 

 Conjugates ; set free in the Diatomacese. 



