(EDOGONIUM, 



[ 551 ] 



CEDOGONIUM. 



cell colourless aud devoid of chlorophyll — 

 above all, by the aimular stride occurring at 

 the euds of 'many of the cells (PI. 9. fig. 7 b, 

 h). The cells have each a large parietal 

 nucleus (fig. 7 a). The large round inter- 

 stitial sporangial cell (fig. 7^) is also a very 

 distiuctive character. The filaments are at- 

 tached, when young, to stones, plants, &c. 

 by root-like processes ; and are composed of 

 rows of cylindrical cells, which multiply 

 interstitially in a very curious manner. 

 When a cell is about to divide, an annular 

 deposit of cellulose occurs around the upper 

 part of the parent cell. Next the wall of 

 the parent cell breaks, by a circumscissile 

 dehiscence, just below the cellulose ring. 

 The internal cell elongates aud removes the 

 margins of the circular slits from each other, 

 the upper piece of the parent-cell wall being 

 pushed up as a kind of cap on the elongating 

 cell. While the cell is thus being elongated, 

 its primordial utricle becomes divided below 

 the line of dehiscence of the parent cell ; 

 but both the new portions grow, so that the 

 line of division between the two new cells 

 at length rises above the margin of the 

 lower part of the parent cell. The annidar 

 deposit of gelatinous cellulose has mean- 

 while become stretched or developed over 

 the space left by the separation of the halves 

 of the parent membrane, forming an outer 

 coat to the new cell. After the growth of 

 the lower cell is finished, the upper one 

 begins to elongate, until it attains equal 

 length ; it remains poor in protoplasm and 

 chlorophyll while growing, but becomes 

 densely tilled when it has attained its full 

 dimensions. The margins or broken ends of 

 the parent-cell wall form the annular striae 

 seen on the filaments (PL 9. fig. 7 b, (/, h) : 

 at first there is only one at the top of any 

 given cell; but the next dehiscence takes 

 place just below this, giving rise to a second, 

 and so on, until many successive rings are 

 produced at one spot. 



The zoospores or ciliated gonidia (fig. 7 c) 

 are formed from the entire contents of a 

 cell, and exhibit a large round nucleus; 

 t'.iey escape by a circumscissile dehiscence 

 of the wall of the parent cell (6) : the fila- 

 ment, however, does not generally become 

 quite broken in two ; the portions remain 

 attached by a strip of the side-wall forming 

 a kind of hinge ; and the zoospores are not 

 set free directly, but at first are enclosed in 

 a very delicate and almost imperceptible 

 globular envelope, colorable blue by iodine 

 and sulphuric acid, which appears to dis- 



solve very quickly in the water. The zoo- 

 spores are large, somewhat ovate in form, 

 with a transparent region at one end, whence 

 the numerous cilia arise. When expelled, 

 they move for a time, and then come to rest, 

 attaching themselves to foreign objects by 

 the ciliated end, acquiring a membrane, 

 sending out root-like processes below {e), 

 and elongating and expanding above into a 

 longish pear-shaped body. Sometimes the 

 zoospores do not completely extricate them- 

 selves from the parent cell, and then ger- 

 minate in this way in situ, the root-like 

 processes remaining engaged in the parent 

 cell. Very often they attach themselves 

 upon the parent filament to germinate. The 

 next stage after germination presents two 

 difTerent classes of phenomena : in the one 

 case, as a purely vegetative zoospore, the 

 young plant elongates gradually into a 

 jointed filament by extension and cell- 

 division ; in the other it is an androspore, 

 and becomes an antheridial filament. 



The (Edoyonia produce large resting- 

 spores (oospores or oogonia), which are 

 formed from the entire contents of the 

 uppermost of two cells developed as above 

 described. A rupture of the parent-cell 

 wall takes place at the side during the 

 development of the spores ; through the 

 small orifice thus formed the spore-mass 

 becomes fertilized through the agency of 

 the little globular bodies produced in the 

 autheridia (PL 5. figs. 5, 16, 17). Ulti- 

 mately the spore, while increasing in size, 

 retracts itself from the walls of its parent 

 cell {oor/oniuiii), and lies free in the cavity, 

 presenting a double coat, the outer of which 

 is thick and tough ; its contents acquire a 

 red colour as it ripens. The parent cell of 

 the spore mostly acquires a globular or 

 elliptical form, and a red or brown colour, 

 appearing like a kind of nodule on the fila- 

 ment ; and the ripe spore, of globular elli|D- 

 tical, or depressed spherical form, is mostly 

 of greater diameter than the ordinary cells 

 (PL 5. fig. 21). The ripe spore, which is 

 quadruple, escapes by the decomposition or 

 dehiscence of the parent cell, and is covered 

 with a hyaline membrane. Each of the 

 four spores is likewise surrounded by its 

 ceU-membrane. After a short time has 

 elapsed, the hyaline membrane disappears, 

 and the four spores lie still and motionless. 

 Then a change sets in : the cell-membrane 

 of each spore bursts by means of an annular 

 slit, and a part separates like a lid. Soon 

 the cell-contents leave the ceU in the form 



