DEVELOPMENT OF PLANTS 



213 



The reproductive organs are formed from short branches as 

 shown in Fig. 147, A. The solution of the walls at the point of 



FIG. 145. 



FIG. 146. 



FIG. 145. Appearance of one of the powdery mildews, Uncinula, on leaf 

 of elm. 



FIG. 146. Enlarged view of the mycelium, ascocarp, etc., of one of the 

 mildews, Erysiphe: c, erect hyphae forming spores or conidia; h } haustoria 

 penetrating epidermis of leaf; a, ascocarp or perithecium. 



D 



FIG. 147. Sexual reproduction of a powdery mildew : A, meeting of the 

 male, an, and female, o, gametangia. B, fertilization, the male gamete, m, 

 is seen approaching the female. C, section of young ascocarp showing the 

 early germination of the gametospore, which has become surrounded by 

 hyphae derived from the mycelium. D, later stage, the gametospore has 

 developed several cells and the terminal one is being transformed into an 

 ascus, as. After Harper. 



