ROOT CHOPS. 



53 



22 D) ; and to reproductive organs (Fig. 22 F) within the 

 host-plant. The protoplasm of the conidia either divides 

 or gives rise to a hypha or " germ tube " (Fig. 23). When 

 it divides it produces a number of zoospores provided with 

 cilia (iilaments) (Fig. 23 B). The zoospores float about 

 in the atmosphere and thereby spread the disease. Ulti- 

 mately the cilia disappear, and the zoospores settle down 

 upon the leaves of the potato plant, giving rise to another 



Fig. 23. — Potato ruNons (Pcronospora iiifi'stans). 



A. Conidiuin dividing. 



B. Conidium producing zoospores (after division). 

 0. Gonidium protruding a filament of protoplasm. 

 D. Oogonium ($) and antheridium ((J). 



B. Oospore (Repting-spore). 



F. Oospore producing zoospores. 



G. Oospore germinating. 



(X aoodiam.) 



generation of mycelia. According to the late Rev. M. J. 

 Berkeley, F.R.S., the mycelium sometimes hibernates 

 and becomes perennial. Sexual reproductive organs are 

 formed from the cells of the mycelium within the host- 

 plant. They are generally to be found in the inter- 

 cellular spaces (Fig. 22 F, and Fig. 23 D). Fertilization 



