UREDINALES 



555 



rupture, laying bare the sorus (Hunter, 1926). In Calyptospora Goepper- 

 tiana, the pycnia are formed normally but the pycnospores regularly abort. 

 In Gallowaya pinicola (B. O. Dodge, 1925) on Pinus virginiana, vestigial 

 pycnia (spermogonia) are formed but they fail to rupture the overlying 

 tissue or to form pycnospores (spermatia). 



Pycnospores are ovoid or spherical, very small (2 to 4^u) or, if bacilli- 

 form, up to 1.6 by 9ju; their membrane is hyaline and smooth; their content 

 poor in cytoplasm and reserve materials; the nucleus is comparatively 

 large, sometimes occupying two-thirds of the cell volume. They accumu- 

 late as a slimy mass in the cavity formed by the periphyses and are 

 repeatedly extruded; in some species, as Cronartium ribicola, Endophyl- 



Fig. 372. — Types of aecia. 1. Caeoma of Phragmidium Rubi. P, paraphyses. 2. 

 Aecidium of Uromyces Erythronii. Per, peridium. (1 X 400; 2 X 300; after Sappin- 

 Trouffy, 1896.) 



lum Sempervivi and Puccinia obtegens (P. suaveolens) , they have a sweetish 

 odor, in Gymnoconia Rosae, an offensive odor. Their further develop- 

 ment is unknown. In some species, e.g., Phragmidium violaceum, they 

 appear to degenerate early (Blackman, 1904); in others, as Cronartium 

 ribicola, they appear to be normal (Colley, 1918). In any case, they 

 seldom germinate and when they do form a short germ tube, it is not 

 capable of producing infection. 



Simultaneously with the pycnospores or shortly thereafter, a second 

 spore form, the aeciospores, usually develops in special sori, the aecia, 

 on the uninucleate mycelium. These belong to two types: the caeoma, 

 which is usually placed directly under the cuticle or epidermis, is broad 

 and flat, naked or covered by periphyses (in the Uredinales, usually called 

 paraphyses, Fig. 372, 1). After its formation it is able to spread laterally 

 and is consequently indefinite in form. In the higher type, the aecidium 

 (or cup type) is placed in the host tissue, several cell layers deep; it is 

 spherical or ellipsoidal and always covered by pseudoperidium, also 



