PARASITIC FUNGI AND MOULDS. 31 



filaments of which these tufts consist display at their 

 extremities the sporangia represented in Fig. 15, 1. 

 On rotten fruits, the spores of these fungi germinate 

 in five or six hours by introducing their hyphse 

 through the epidermis. Sleepiness, which is only the 

 first stage of rottenness, is, according to Davaine, 

 to be ascribed to the action of these fungi. Fruit in 

 this mouldy condition is sometimes unwholesome. 



The potato-fungus, Peronospora infestans, is one 

 of the most dreaded scourges of this valuable plant. 

 It attacks the lower surface of the leaves and stalks, 

 and appears in the month of July, in the form of 

 brown patches. The long hyphse penetrate deeply 

 beneath the epidermis, and will even propagate them- 

 selves on the tubers. 



Among the causes which produce or promote this 

 disease, agriculturists place the excessive moisture 

 of the soil, setting the plants too late in the season, 

 the use of bad seed, the premature and exhausting 

 germination of the tubers before they are planted, 

 and the use of fresh dung which is not sufficiently 

 decomposed. 



The following process is indicated as likely to 

 prevent the development of this parasite. In the 

 spring, the first protective ridge should be prepared 

 with a flat top, from eight to ten centimetres high, 

 and from twenty-five to thirty centimetres wide. 

 In the first fortnight of August, a second protective 

 ridge should be earthed up, of which the edge should 



