206 



MANUAL OF POISONOUS PLANTS 



side of the oogonium ; the antheridium. This pierces the oogonium and the 

 protoplasm of the antheridium passes into the oosphere. 



In the species that have been studied like Peronospora parasitica, and Al- 

 bugo Candida, the oosphere or egg cell contains a single nucleus, situated about 

 at the center, the remaining nuclei having passed into the peripheral layer of the 

 protoplasm of the periplasm. 



A single male nucleus passes from the antheridium into the egg cell and 

 fuses with the nucleus of the egg cell. Numerous investigations in this line 

 have been made by Stevens,* Berlese,f and Wager.$ It is probable that the 

 course of reproduction is similar for other species. 



In fertilization karyokinetic changes occur. The protoplasm surrounding 

 the oosphere is used to build up the wall of the oospore. Germination of 

 oospore probably takes place in the spring. In Albugo or Cystopus the conidia 

 are borne in a moniliform chain. 



400- 



Fig. 50. Downy Mildew of Clover (Peronospora 

 trifoliorum). a. Conidiophore. c. Stoma. b. Con- 

 idium; common in Europe on Red Clover, may be in- 

 jurious to animals. After Smith. 



* Bot. Gaz. 28:149; 23:77; 34:420. 

 tjahrb. f. wiss. Bot. 31:159. 

 } Annals of Bot. 4:127; 14:263. 



