ROOT CROPS. 



59 



become round. The spores may germinate immediately 

 or become spinulose (Fig. 24 A) and hibernate for some 

 time. The spores give rise to mycelia when circumstances 

 are favourable for their development and growth. 



Prevention. — Burn all infested- matter, and plant pota- 

 toes free from disease. 



The Irish (?) Potato Fungus {Peziza postuma, 



Fig. 25. — Peziza postuma [a potato fungus). 



A. The fangus growing from a Sclerotium (2) ; at 1 is the pileus or cup-like 



head (nat. size). 



B. Diagram of upper part of pileus, showing the " perpendicular cells." 



C. The contents of a " perpendicular cell." (1) Ascus containing spores 



(sporidia). (2) A paraphysis (x 200). 



D. Stem of potato plant with nodular sclerotia (nat. size). 



Fig. 25) was iirst observed in the West of Ireland in 1880, 

 and a description of it appeared in the Gardeners' 

 Chronicle for August 20th, 1880. It produces nodular 

 growths upon and within the stems and leaves of the 

 potato plant (Fig. 25 D). Unlike Peronospora, this fun- 

 gus does not cause putrefactive changes to occur within 

 the tissues of the host-plant, but extracts the sap, etc., 

 of the stems and leaves, which finally become dry and 



