GROUP I. THALLOPHYTA : ALG). 225 



Monospora (Rhodophyceae), and bj Vaucheria geminatct^ and some- 

 times by other species of Vaucheria (Chlorophyceae). Reproduc- 

 tion by means of asexually-produced spores or gonidia occurs with 

 but few exceptions (e.g. Conjugate^ Fucaceae, Characeae). Sexual 

 reproduction is general throughout the class, though it has not yet 

 been observed in all forms ; it appears to be definitively absent 

 in the Cyanophycese, and in some of the lower Chlorophyceae (e.g. 

 some unicellular Protococcoideee) and Phaeophyceae (Syngeneticae); 



FIG. 162. A portion of the body of Caulerpa plumaris showing dor si ventral arrangement 

 of members. The horizontal stem bears leaves on its upper (dorsal) surface, and roots on 

 its lower (ventral) surface. 



There are various modes of sexual reproduction in the group. 

 The following is an enumeration of them (see also p. 80) : 



I. Isogamy : 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 riot ciliated (aplanogametes) ; not set free in the 

 Conjugate ; set free in the Diatomaceaev 



II. Heterogamy : 



(a) Oogamy : the female organ is an oogonium ; the sexual 

 cells are spermatozoids and oospheres, the former ciliated and 

 free-swimming, the latter not ciliated but sometimes free-floating ; 

 process, fertilisation; product, an oosporej (e.g. Volvox, Vaucheria, 

 (Edogonium, Coleochaete, Characeae, Fucaceae). 



(6) Carpogamy ; the female organ is a procarp in which no 

 female cell is differentiated ; male cell free, not ciliated, a sperma- 



V. S. B. Q 



