CH. X] 



THE TUBULAR AI/LE 



431 



all of the nuclei except one having passed meantime into the 



main filament. Close alongside, and in some kinds from the 



same stalk, is formed a smaller tubular branch from which is 



cut off a terminal antheridium, wherein are developed numer- 



ous ciliate sperm cells. The one of these which first gains 



entrance to the oogonium, through a special opening which 



appears, fertilizes the egg cell, wherefrom there develops 



a thick-walled resting 



oospore, which later 



germinates to a new 



filament. These oogo- 



nia and antheridia are 



of special interest as 



the first structures met 



in the ascending scale 



which are devoted spe- 



cially to the formation 



and fusion of the sexual 



cells; for in all lower 



forms the cells which 



produce the reproduc- 



tive bodies are only 



transformed vegetative 



Cells. Another common 



form k Rnlr 

 .S VOir 



299), which grOWS 



n 



FlG 299 _ Botrydium gra nuiatum. 



Left, an adult individual ; next, individual 

 P roducin S and expelling zoospores ; next, be- 

 i OW)VOUngplant germinating from a zoospore; 

 all X 25. Above, right, a zoospore, with 



masses upon wet, clayey two chlor P lasts J x soo. (After L. Kny.) 

 earth, especially when drying from a flooded condition. The 

 single plants, each about the size of a pin head, are balloon 

 shaped, the lower part being differentiated into colorless 

 rhizoids which enter the earth and there absorb water and 

 mineral salts for the green part in the light ; and herein is 

 anticipated the physiological differentiation into root and 

 shoot prevailing in the higher plants. It reproduces asexu- 

 ally by zoospores, which are formed in great numbers, and also 

 sexually by conjugation of small biciliate isogametes. 



