452 SYSTEMATIC BOTANY. 



temporarily), red colour, -reproduced by zoospores discharged from 

 the ordinary cells of the thallus (A, d\ or by spores formed in 

 these cells after impregnation by combination of the contents of 

 two cells, either by conjugation (C, e), or by the transference of 

 spermatozoids into the parent cell of the spore, the spores (C, d} 

 passing through a stage of rest before germination. Illustrative 

 Genera : Codium, Stackh. ; Bryopsis, Lamx. ; Vaucheria, DC. ; 

 Botrydium, Wallr. ; Drapamaldia, Bory ; (Edoyonmm, Link ; 

 Spirogyra, Link ; Sphccroplea, Agh. ; Coleochcete, Breb. ; Hydro- 

 dictyon, Roth. ; Ulva, Agh. ; Tetraspora, Dec. ; Nostoc, Yauch. ; 

 Botrydina, Breb. ; Clathrocystis, Henf . ; Palmetta, Agh. ; (Achlya, 

 Nees) ; (Chytridium, Al. Br.). 



Structure and Life-history. The specialities of the very multiform group 

 represented by the above list of genera can scarcely be dealt with in a work 

 like the present ; and, in fact, our knowledge of the essential characters 

 of the plants is at the present time undergoing a thoroup-h revision. In 

 the definition of the group of Confervoids here, the Oscillatoriaceae and 

 the other permanently active forms are excluded. The Oscillatoriaceae 

 are organized in a very different way from the true Confervoids. The 

 Confervoids proper are mostly very simple cellular organisms, with chlo- 

 rophyll and starch in the cells while they are actively vegetating ; the 

 majority discharge the cell-contents in the shape of one or many active 

 zoospores, with 2 or more cilia at a beak-like extremity ( Vaucheria, fig. 506, 

 p. 442), or with cilia all over the surface ; besides which process, sexual 

 reproduction has been observed in Zyynema by conjugation, in (Edogo- 

 nium, Sph&roplea, Vaucheria, Bulboclicete, &c. by spermatozoids derived 

 from one cell entering the cavity of the parent cell of the spore ; and in all 

 probability this will be found general. The mode of fertilization will be 

 found described at p. 441. The spores formed after fertilization become 

 encysted in a firm coat, thrown off in germination, which commonly ensues 

 only after a long interval. The Palmellece are forms not yet well explained, 

 composed of solitary cells imbedded in a common mucus ; they appear to 

 stand at the lowest point of organization in the Vegetable Kingdom, if 

 they be not stages of growth of higher forms (fig. 504, p. 437). 



The genera above grouped by Professor Henfrey under the head of 

 Confervoidese are more naturally grouped by Decaisne under several 

 distinct sections of varying degrees of importance as follows : 



1. Conferva, comprising plants consisting of tubes or cells containing 

 ovoid spores provided with 2-4 vibratile cilia. 



2. Unicellular es. Plants consisting of a single cell producing numerous 

 ciliated spores, which in Botrydium unite by conjugation (fig. 503, E). 



3. CEdoyomecs. Filamentous Algae, producing spores either by the ag- 

 gregation of the green colouring-matter of the cell into a spheroidal mass, 

 w r hich escapes from the parent cell by a special aperture in its wall, and 

 is then seen to be provided with a crown of vibratile cilia, or as the result 

 of sexual agency. The antheridia consist of filaments, each cell of which 

 contains 1 or 2 spermatozoids, w r hich escape by the lifting of a lid -like 

 valve of the cell- wall and fertilize the spore as above stated (see p. 441 



