84 



THE PHYCOMYCETES 



ovate in shape. At maturity a pore is formed at the tip of the 

 sporangium; the zoospores creep through the pore in an amoe- 

 boid fashion, adhering to the mouth of the sporangium for a time, 

 and finally swim away. The zoospores are provided with a 

 single slender cilium, posterior in position. Both in its ciliation 

 and internal structure, the zoospores of Monoblepharis are very 

 similar to those of the Blastocladiales. Each germinates by two 

 germ tubes, one of which forms the rhizoidal system and the 

 other the main hvphae. 



Fig. 24. Fertilization and emergence of the oospore of Monoblepharis 

 polymorpha. A. The small uniciliate sperm lodged at the receptive spot 

 on the oogonium. B. Fusion has begun. C. Fusion has been completed. 

 (This process, A to C, may require less than 10 minutes.) D. Mature 

 thick-walled oospore, such as may be noted after several hours. (Adapted 



from Barnes and Melville.) 



Considerable specific variation occurs in connection with the 

 sexual reproductive structures. In M. polymorpha, for example, 

 the antheridia are exserted on the oogonia (epigynous); whereas 

 in M. sphaerica and M. mcicrandra the antheridia are hypogynous. 

 The development of the antheridia and the maturation of the 

 antherozoids occur in a manner very similar to those of the zoo- 

 spores; the antherozoids are smaller than the zoospores and have 

 a more pronounced amoeboid movement but otherwise resemble 

 them very closely. 



The content of the oog^onium becomes a sins^le egrg. When it 

 is mature, a receptive papilla is formed on the wall of the oogoni- 

 um, providing a point of entrance for the sperm. Immediately 

 after fertilization the t^g becomes extruded from the oogonium 



