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 hyphze 
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 hyphez 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 
