Coleochsetaceae 317 



in several species, and more recently, and in greater detail, by Oltmanns ('98) 

 in C. pulvinata. The antheridia are flask-shaped (fig. 208, 2 and 3 a) and 

 are usually developed in groups, either terminally on the branches, or, in the 

 discoidal species, sometimes in the vicinity of the oogonium. They are, as a 

 rule, colourless and each one gives origin to a single ovoid antherozoid with 

 two cilia. This antherozoid is in most species colourless, but is green in 

 C. scutata. Moreover, in this species the antherozoids apparently arise by 

 the divisions of the contents of ordinary disc- cells. The oogonium is formed 

 by the swelling of the terminal cell of a short branch. In C. scutata, 

 C. orbicularis, and others, the adjacent branches continue their growth and 

 the oogonia are gradually enclosed within the disc. In these species the 

 oogonia are depressed with a bottle-neck-like trichogyne, but in C. pulvinata 

 the oogonium is bottle-shaped with a long cylindrical trichogyne (fig. 208, 

 4 and 5 o). In the discoidal species the oogonia frequently exhibit a zonal 

 arrangement. The young oogonium possesses a relatively large nucleus and 

 one chloroplast. One oosphere is formed within the swollen oogonium and 

 when ready for fertilization it contains a conspicuous chloroplast. Just 

 before fertilization the trichogyne opens at the apex and exudes a small 

 quantity of mucus. According to Lewis ('07) the male nucleus of 

 C. Nitellarum, when within the egg-cell, increases in size as it approaches 

 the female nucleus and just before fusion the two nuclei are of approximately 

 the same diameter. 



After fertilization the oospore surrounds itself with a wall and grows 

 much in size. When nuclear fusion has taken place the oogonium 

 becomes closely covered with a layer of cortical cells produced by the 

 proliferation of the supporting-cell and other adjacent cells of the thallus. 

 The entire spherical (or spherical-depressed) structure resulting from fertili- 

 zation is known as a ' spermocarp,' and the cortical cells generally lose their 

 green colour and become brown or brownish red. The spermocarps remain 

 dormant through the winter. 



On germination the oospore divides first into octants, and then into 

 16 or 32 cells. As this division proceeds, the wall of the spermocarp splits 

 into two halves (fig. 208 8), and each of the newly formed cells either 

 becomes itself a ' swarm-cell ' or gives origin to a ' swarm-cell/ which differs 

 much from the ordinary zoogonidium both in shape and in the attachment 

 of the cilia. When it comes to rest the ' swarm-cell ' germinates to form a 

 small asexual plant, often of only a few cells, which is sometimes followed by 

 several asexual generations of equally small plants before a sexual plant is 

 finally developed. 



It was Pringsheim ('60) who originally pointed out that in Coleoch&te there appeared 

 to be an alternation of generations and that the development of the 'swarm-spores' formed 

 on the germination of the oospore into small asexual plants probably represented a 



