THE FUNGI WHICH CAUSE PLANT DISEASE 349 



12-18 X 16-30 m; walls pale-yellow, rather thin, 1-1.5 n; sparsely 

 echinulate with short conical points. 



III. Telia hypophyllous, on whitish or pale reddish spots; 

 tehospores within the epidermal cells, 1-celled, short-cylindrical 

 or polygonal, 13-20 /i broad; wall colorless, smooth, thin. 



I ( =Peridermium elatinum) on fir causing sweUing, cankers and 

 witches' brooms. 



II and III on various members of the pink family. 



All stages possess perennating mycelium. The aecial stage 

 is of most economic significance, producing witches' brooms of 

 various sizes. The secia are formed only on the deformed needles 

 of the witches' brooms. 



Melampsoropsis (Schroter) Arthur (p. 341) 



Cycle of development includes pycnia, secia, uredinia and telia, 

 with distinct alternating phases; heteroecious. Pycnia and other 

 sori subepidermal. 



0. Pycnia deep-seated, somewhat erumpent, flask-shaped. 



1. .^cia erumpent, flattened laterally. Peridium firm, outer 

 wall of cells greatly thickened and transversely striate, inner wall 

 smooth. iEciospores ellipsoid to globoid; wall colorless, coarsely 

 verrucose with deciduous tubercles. 



II. Uredinia erumpent, pulverulent. Peridium very delicate, 

 evanescent, sometimes wanting. Urediniospores catenulate, 

 globoid to lanceolate; wall colorless, verrucose with somewhat 

 deciduous tubercles, pores obscure. 



III. Telia erumpent, definite, roundish, waxy becoming vel- 

 vety. Teliospores catenulate, 1-celled, oblong or cuboid; wall 

 colorless, thin, smooth. 



M. rhododendri (D. C.) Arth. 



Uredinial and telial stages on Rhododendrons; pycnial and 

 aecial stages (=iEcidium abietinum) on Picea excelsa. 



The pycnia appear on fir leaves in spring and about a month 

 later the aecia. The seciospores germinate upon the Rhododen- 

 dron. The mycelium perennates in its evergreen leaves and 

 produces the uredinial and telial stages, the former of which 

 serves for dissemination. The basidiospores infect the young fir 

 leaves. 



