ENTOMOLOGY. 



413 



(Fig-. 2, c), which are colorless and globose. When ripe these spores 

 rupture the free end of the ascus and escape, indicating- that the 

 fungus is only too able to propag-ate rapidl3\ When we look at the 

 surface of a sing-le pocket, we can observe countless numbers of 

 asci, and as each contains eig-ht spores, the propag-ation, and with 

 it the distribution, is very rapid; and j^et no one has been able to 

 infect healthy plums with such spores. As the mycelium of the 

 fung-us can be detected in the smaller twig-s of the tree early in the 

 spring- we can be certain that it can live in its host from year to 

 j^ear. 



We have but one remedy that has proved to be effective, but it is 

 one that requires much labor. If the bladders are removed while 

 still 3'oung-, and if we cut back the twig^s and smaller branches, we 

 can succeed in eradicating- the disease in two or three years. 



Powdery Mildew (Fig. 3.) 

 ( Podosphieca oxycantha ( D. C.) De Barry.) 



Fig. 3. Powdery Mildew; e, blotch of mildew, natural size; c, mycelium 

 forming summer-spores; b.haustoria of mycelium abstracting cell-sap from leaf; 

 a, perithecium; d, spore cavity: all enlarged. 



This disease starts rather late in the season and is frequently very 

 abundant in the latter part of summer and autumn. It appears as 

 white blotches upon young- leaves and tender shoots; these blotches 

 (Fig. 3, e) spread rapidly and frequently cover the entire leaf. The 

 threads, composing the blotches, branch and cross in all possible 

 manner, and form a true felt (Fig. 3, c). The denser portion of it is 

 covered with white powder and very minute, black, globular objects 

 (Fig. 3, a). Both sides of the leaf are affected. Upon older leaves the 

 injury is slight, but the growing tips and young leaves are ruined. 

 This white felt is the mycelium or vegetative part of the parasitic 

 plant. The threads that form it do not enter the host, but abstract 

 food from it by small suckers or haustoria (Fig. 3, b). The spores 

 (conidia, or summer-spores) form upon the ends of thicker branches 

 (Fig. 3, c) and if they reach a proper place for germination, they start 



