306 FUNGOUS DISEASES OF PLANTS 



which, in its general characters, as regards spores (size, shape, etc.), 

 is very much like the Alternaria Solani producing the early blight 

 of potatoes. The fungus is a genuine parasite, attacking plants 

 both young and old, and apparently under all conditions, although 

 the disease becomes epidemic only in hot rainy weather. 



The parasite attacks all of the parts of the plant above ground, 

 but never affects the roots. During epidemic periods the disease 

 works with great rapidity, so that the tops of plants in an entire 

 garden may be entirely destroyed within a few days. The disease 

 first makes its appearance as dead brown streaks or cankers on 

 the stems of the plants near the ground. This is the primary in- 

 fection in the spring, and it is probably brought about through 

 spores that have wintered over on the mulch or debris on the 

 soil, the stems becoming infected as they come through the 

 ground. This first stage is usually overlooked by the grower 

 unless it becomes severe enough to cause the breaking over 

 of the stems, which sometimes happens. Ordinarily the first 

 observed appearance of the disease is on the leaves, which show 

 rather large, more or less circular, watery spots. The tissue is 

 killed outright in those spots and later becomes dry and papery 

 with a brown or yellowish center. Under favorable weather con- 

 ditions .these spots spread and coalesce, readily killing the leaves 

 and the entire top of the plant (Figs. 138, 139), so that a badly 

 blighted plantation looks as if it had been drenched with scalding 

 water. If the berries set before the blight has become destructive, 

 they may be attacked and blasted, turning brown and dropping off 

 before they can ripen. 



The fungus. The conidia or spores of the parasite are pro- 

 duced in great abundance on all parts of the affected plants, but 

 particularly so on the stems and blasted berries. No perfect or 

 winter stage has been discovered for the fungus, but the fact that 

 the spores will germinate after remaining in the laboratory dry for 

 three months indicates that the conidia of the fungus are prob- 

 ably carried over winter on the mulch or debris on the beds. It 

 grows very readily as a saprophyte, and may pass the winter 

 growing on the dead stems and mulch on the bed. The fungus 

 makes its first appearance on the stems early in the spring, shortly 

 after they are up, but the disease does not become destructive 



