CONFERVOIDE^ HETEROGAMY 



223 



first described by A. Braun as the ' rejuvenescence ' of a cell, i.e. the 

 transformation of the entire protoplasm of a vegetative cell into a 

 ' primordial ceiy which subsequently invests itself with a new cell-wall, 

 and forms the starting-point of the life of a new individual. In some 

 one cell of a filament, either the terminal or some other, sometimes 

 even in the single cell of which a young filament is composed, the proto- 

 plasm contracts into a globular body which 

 ultimately becomes free by the rupture of the 

 cell-wall, by a transverse slit, into two very un- 

 equal halves. . When this takes place in the 

 terminal cell of a filament or the single cell of 

 a young individual, the upper smaller portion 

 of the cell-wall is lifted up like a lid, or even 

 completely thrown off like a cap. The zoospore 

 thus formed, which in some species is one of 

 the largest and most striking known, has a 

 nucleus, a red ' pigment-spot,' and an anterior 

 hyaline region, to which is attached a tuft of 

 cilia, visible even before its escape from its 

 mother-cell. At the period of escape it is still 

 enveloped in a transparent membrane, which, 

 however, it soon breaks through, and then moves 

 about in the water with great velocity for 

 perhaps half an hour, displaying at this period a 

 number of vacuoles. On coming to rest, the 

 zoospore becomes attached by its anterior hya- 

 line end, loses its cilia, invests itself with a 

 cell-wall, puts out a rhizoid from the point of 

 attachment, and develops into a filament with 

 transverse septa. From the position occupied 

 by the zoospore in the mother-cell, the direc- 

 tion of growth of the new individual must be 

 at right angles to that of the parent-filament. 

 Many of the plants which spring from zoospores 

 are non-sexual, producing nothing but zoospores. 

 CEdogonium is also reproduced by resting-sporei (Wille, Bot. Gesell. 

 Stockholm, Sept. 26, 1883; see Bot. Centralbl., xvi., 1883, p. 215). 



The sexual reproduction of CEdogonium still shows a high degree of 

 differentiation of the male and female elements. The antherozoids are 

 very similar in form to the zoospores, but much smaller, and they are 

 provided with a similar tuft of cilia. The antherids are cells belonging 

 to ordinary filaments, but shorter and not containing so much chlorophyll 



Fig. 200. — Portion of filament 

 qX CEdogonium. win^jthe 

 cushion of cellulose which 

 has lengthened to the piece 

 of cell-wall, _7y' in B\ c, cell- 

 caps (magnified). ■ - 



