27 



There are two forms of reproduction, non-sexual and sexual. In the 

 first the contents of certain cells escape in the form of large zoospores 

 (Fig. 16, C), of oval form, having the smaller end colorless and surrounded 

 by a crown of cilia. After a short period of active motion, the zoospore 

 comes to rest, secretes a cell wall about itself, and the transparent end 

 becomes flattened out 

 into a disc (", tZ), by 

 which it fastens itself 

 to some object in the 

 water. The upper part 

 now rapidly elongates, 

 and dividing repeat- 

 edly by cross walls, 

 develops into a fila- 

 ment like the original 

 one. In many species 

 special zoospores are 

 formed, smaller than 

 the ordinary ones, that 

 attach themselves to 

 the filaments bearing 

 the female reproduc- 

 tive organ (oogonium), 

 and grow into small 

 plants bearing the 

 male organ (antherid- 

 ium), (Fig. 16, B}. 



The sexual repro- 

 duction takes place as 

 follows : Certain cells 

 of a filament become 

 distinguished by their 

 denser contents and 

 by an increase in size, 

 becoming oval or nearly globular in form (Fig. 16, A, B). When fully 

 grown, the contents contract and form a naked cell, which sometimes 

 shows a clear area at one point on the surface. This globular mass of 

 protoplasm is the egg cell, or female cell, and the cell containing it is 

 called the " oogonium." When the egg cell is ripe, the oogonium opens 

 by means of a little pore at one side (Fig. 16, A). 



In other cells, either of the same filament or else of the small male 



an. 



FIG. 16. A, portion of a filament of (Edogonium, 

 with two oogonia (o</.). The lower one shows the 

 opening. B, a similar filament, to which is at- 

 tached a small male plant with an antheridium 

 (an.). C, a zoospore of (Edoc/onium. D, a similar 

 spore germinating. E, base of a filament showing 

 the disc (d) by which it is attached. F, another 

 species of CEdoyonium with a ripe spore (sp.) G, 

 part of a plant of Bulbochsete. C, D, x 300; the 

 others x 150. 



