I a, THALLOPHYTES. 



ery numerous but short, and cover the whole surface of the swarm-spore (Vaucheria), 

 ^hile sometimes they form a crest round the hyahne part (CEdogonium), but are 

 lost often fixed in pairs to the anterior margin and are then very long. Some- 

 mes swarm-spores are of two sizes (Macro- and Micro-gonidia), indicating perhaps 

 sexual relationship as yet undemonstrated. 



Sexual Reproduction is brought about in very different ways, the most im- 

 ortant distinction being that the sexual cells may be either similar or dissimilar. 

 Q the first case the sexual reproduction is called Conjugation, in the second 

 ase Fertilisation or Impregnation. Conjugation occurs in Ulothrix^, Chlamydo- 

 occus, Pandorina, and probably also in other Volvocineae, by the coalescence 

 f two free - swimming cells which perfectly resemble ordinary swarm -spores. 

 n the conjugation of the Conjugatae and Diatomacese, on the contrary, the 

 Dnjugating cells are stationary ; they are sometimes expelled in the form of 

 rimordial cells, and subsequently unite. But usually the walls of the cells con- 

 srned grow together, and their contents are reconstructed as primordial cells, 

 ne then passing over into the other and uniting with it. The product of this 

 Dalescence surrounds itself with a firm cell-wall, and is called a Zygospore; it 

 enerally germinates only after a long period of rest. Fertilisation, in the narrower 

 ^nse of the term, is, except in the Florideae, brought about by Oogonia and Anthe- 

 dia. Oogonia are cells in which the female reproductive bodies or Oospheres 

 re formed ; the Antheridia are cells or masses of cells which produce the male 

 ^productive bodies or Spermatozoids. The oospheres are formed, in Fucaceae, 

 iveral in one oogonium, out of which they are expelled before fertilisation ; but 

 1 the other groups the whole contents of the oogonium are transformed into one 

 osphere, which contracts, becomes loosened from the cell-wall, and constitutes a 

 rimordial cell. This remains motionless within the wall of the oogonium, and there 

 waits the arrival of the spermatozoids, which enter by an opening previously formed 

 1 the wall of the oogonium, and unite with the oosphere. The part of the oosphere 

 hich faces the opening is hyaline, and takes up the spermatozoids; sometimes a 

 yaline mass of mucilage is expelled by the anterior end of the oosphere from the 

 Dgonium before fertilisation. The spermatozoids of Algge which do not belong to 

 le class Florideae resemble swarm-spores, but are usually much smaller and provided 

 ith a red corpuscle ; they swarm out of the antheridia, and some of them finally , 

 ;ach the oospheres, with which they coalesce. The oospheres are usually many hun- 

 red or even some thousand times larger than the spermatozoids. Algae are distin- 

 uished from the rest of Cryptogams by their spermatozoids never being in the form 

 f slender spiral filaments, but short, and rounded at least at their posterior end. 



The sexual reproduction of the Florideae differs greatly from that of most 

 ther Algae, but the section of Nemalieae forms the transition to Coleochaete. The 

 Qtheridia of the Florideae produce an immense number of small spermatozoids, 

 hich have no active motion, but are washed about by the water until at length 

 3me of them become attached to a Trichogyne, and empty their contents into 



The term Trichogyne is given to a long thin hair-like hyaline sac, which 

 srves as a receptive organ, and springs from a structure which is called the 



^ Cramer, Bot. Zeitg. 1871, p. 76. (See under Volvocinese.) 



