ALGAE.— SIPIIONEAE. 



33 



branch which has swollen to an oval shape are cut off behind by a cross wall, and con- 

 tract and form a new membrane, and the brood-cell thus formed is either set free by the 

 decomposition of the mother-cell-wall, or falls off with it, and germinates after some 

 days. The brood-cells of V. hamata are formed in the same way, but are thrown out 

 with a jerk, lie quietly where they fall, and germinate during the ensuing night. In other 

 species (V. scssilis, scricea, pjloboloides) the contents of a branch are cut off behind by 

 a septum, contract, and force their way out as a swarm-cell through a fissure at the 

 extremity of the branch. The motion of a swarm-cell lasts only from half a minute to 

 a minute and a half in V. sericea, in other species for some hours. In V. sessilis the 

 rotation of the swarm-cell begins as it leaves the branch, and if the opening of the 

 mother-cell is too small the swarm-cell breaks up into two portions, each of which 

 becomes rounded off and is again a perfect swarm-cell ; but the outer one swims 

 away, the other remains rotating in the mother-cell. These motile cells are the largest 

 known, being visible to the naked eye, and are thickly covered with cilia. Numerous 

 nuclei may be seen in the superficial layer of their protoplasm, and a membrane is 

 secreted on their surface while they are in the motile state. 



B 





Fig. 15 Vancheria sessilis. A, B formation of an antheridiuni a on the branch /;. and of tlie oogonium og. 

 C oogonium opened and ejecting a drop of mucilage st. D spermatozoids. K collection of spermatozoids at the beak 

 of the oogonium F ; a an antheridium emptied of its contents, osp oospore in the oogonium. A, B, li, F from nature, 

 C, D after Pringsheim. 



The formation of the swarm-spores or brood-cells begins in the night, as is the case 

 with most Algae and Fungi ; they escape in the morning, and germination begins during 

 the day or in the following night. In germination one or two green tubular cells are 

 put out (Fig. 14, C, Z*), or a root-like organ of attachment is formed at the same time 

 {E, F, w).— The oogonia and antheridia appear first as lateral protuberances on a fila- 

 ment containing chlorophyll (Fig. i^ F, 15 A, B), sometimes even on the germinating 

 tube of a swarm-cell. All Vaucherias are monoecious, and the two kinds of sexual 

 organs are usually close together. The ant/ieridta (Fig. 15, //, a) are the terminal cells 

 of slender branches, the contents of which, ccmtaining but little chlorophyll, produce a 

 large number of small spcrmatosoids (Fig. 15, D), which escape by the bursting of the 

 antheridial cell at its apex. In several species the antheridia are curved like a horn, in 

 [2] 



