134 BOTANY. 



the female organ consists of a rounded germ-cell situated 

 within a cavity — the oogone; it is developed from one of 

 the cells (sometimes two) of the filament by a condensing 

 and rounding off of the protoplasmic contents; when the 

 germ-cell is fully mature, an opening is formed in the 

 oogone-wall for the ingress of the antherozoids {A and -S, 

 Fig. 62). One or more antherozoids are produced in cer- 

 tain small cells of the same or another filament; in shape 

 they resemble the zoospores mentioned above. Upon es- 

 caping into the water they swim about vigorously, eventu- 

 ally making their way through the opening in the oogone, 

 and then burying themselves in the substance of the germ- 

 cell (J?, s, Fig. 62). After fertilization, the germ-cell be- 

 comes covered with a thick and colored (brown or red) 

 coat, and it then becomes a resting spore, 



279. After a period of rest, the resting spore germinates 

 by rupturing its thick coat and permitting the escape of 

 the contents, enclosed in a thin envelope; by this time the 

 protoplasm has divided into four portions, which take on 

 an oval form and develop a crown of cilia. They soon 

 escape from the investing membrane, and after a brief 

 period of activity grow into an ordinary filament in exactly 

 the same manner as the zoospores. 



Practical Studies. — (a) In midsummer collect a few quarts of the 

 surface-water of weedy ponds, together with the Pond Scums grow- 

 ing therein; put it into a shallow dish, and after an liour or so look 

 carefully (with the naked eye) for Volvox. It will be seen as a minute 

 green ball (from .5 to 1 millimetre in diameter) rolling slowly through 

 the water. Now carefully transfer it to a slide along with enough 

 Pond Scum to prevent crushing. Under even a low power many of 

 the details of structure may be made out, and one or more young 

 colonies in the interior may almost invariably be seen. 



(b) Specimens of CEdogonium may be obtained by examining the 

 small sticks and stems of aquatic plants from quiet waters. They 

 may be recognized by the enlarged cells (obgones). 



