146 



MUkFHuLOGY. 



Growth takes place, not in all parts ot the thread, hut is localized at the ends 

 uf the thn_-ad and its branchi.-s. This represent^ a di^-tinit .idv.m.u- on such 

 u plant as spirog^ra. A^ain, onlv specialized parts ol' the plant in vautheria 

 form the sexual organs. These are short branches, h'arther there is a threat 

 dinference in the size of the two origans, and especially in the size of the 

 gametes, the supphdng gametes (spcrmatozoids) being \'ery minute, 

 while the receptive gamete is hirge and contains all the nutriment for the 

 fertilized egg. In spirog}Ta. on the other harnh there is usually no difler- 

 ence in size of the gametes, as we have seen, and each contributes equall_\' in 

 the matter of nutriment for the fertilized egg. Vaucheri.t, therefore, rep- 

 resents a distinct advance, nut onlv in the vegetative condition ot the plant, 

 but in the specialization of the sexual organs. Vaucheria, witli otlier related 

 algae, belongs to a group known as the Siphou-is, so called because the plants 

 are tube-like or siphon-liko,. 



308. Botrydium granulatura, — An example of one of the simpler 



members of the Siphon c;e is 

 Botrydium granulatum. It is 

 found sometimes in abundance 

 on wet gruunfl which is colored 

 green or red by its presence, 

 according to the stage of de- 

 velopment. The ])lant body is 

 long pear-shaped, the smaller 

 end attached to the ground In- 

 slender branched rhizoids (Fig. 

 14;^). The protoplasm contains 

 manv nuclei and lines the inside 

 of the wall. When multiplication 

 takes place hirge numbers of 

 small zoos[.)ores with one cilium 

 each are formed in the proto- 

 plasm, and escape at free emb 

 Reproduction takes place bv 

 two-ciliated gametes, which fuse 

 in pairs to form zvgospores. In 

 drv seasi">ns the protoplasm in 

 the pear-shaped plant ]>asses 

 down irito the rhizoids and 

 lorms small rtivmdi'd ['hiiiosporcs. 

 All the stages of development arc too (.omplicated to describe here. 



.4, the ^vh(.ae 



lig. 143,1. 

 Botrydium granulatum 

 plant; B, swarm spore; C, plan.igamett-s 

 a single gamete; b-c, two gametes in pri 



