THE FUNGI WHICH CAUSE PLANT DISEASE 343 



II. Uredinia amphigenous and caulicolous, scattered or some- 

 what gregarious, often crowded, round or on stems elongate, 

 0.3-0.5 mm. across, soon naked, reddish-yellow fading to nearly 

 white, pulverulent, ruptured epidermis noticeable; spores broadly 

 elliptical or obovate, 13-18 x 15-25 n, wall colorless, rather thin, 

 2 II, evenly and finely verrucose, with low papillae, pores equa- 

 torial, obscure; paraphyses intermixed with the spores, capitate, 

 large, 5-22 x 40-65 m, smooth, wall thick. 



III. Telia amphigenous and caulicolous, scattered, often con- 

 fluent, round or elongate, 0.2-0.5 mm. across, slightly elevated, 

 reddish-brown becoming blackish; spores subepidermal, appressed 

 into a single layer, prismatic, 1-celled, 10-20 x 42-50 /x; wall 

 brown, smooth, thin, about 1 fi, not thickened above. 



AutcEcious on flax. Sometimes very injurious.^' 

 M. medusae Thiim. 



0. Pycnia chiefly epiphyllousy- scattered or somewhat gregarious, 

 minute, punctiform, pale-yellow, inconspicuous, subcuticular, 

 hemispherical, 40-80 ix in diameter, half as high. 



1. iEcia chiefly hypophyllous, scattered or somewhat grega^ 

 rious, small, 0.1-0.3 nun. broad, round or oblong, pale-yellow 

 fading to white, inconspicuous, formed between epidermis and 

 mesophyll, soon naked, pulverulent, ruptured epidermis notice- 

 able; seciospores globoid, 17-22 by 17-24 /x; wall colorless, thick, 

 2.5-3 II, minutely verrucose, with minute crowded papillae, pores 

 indistinct. 



II. Uredinia amphigenous, or only hypophyllous, scattered, 

 roundish, small, 0.2-0.4 mm. across, early naked, somewhat pul- 

 verulent, orange-yellow, fading to pale brownish-yellow, ruptured 

 epidermis usually inconspicuous; urediniospores ellipsoid or 

 obovate-ellipsoid, 15-18 by 22-30 y,, usually flattened laterally; 

 wall colorless, 2.5-3 n or up to 10 ii on the flattened sides, sparsely 

 and evenly verrucose, with fine papillae, except on the flattened 

 sides which are smooth; paraphyses numerous, intermixed with 

 the spores, capitate, smooth, 40-65 ix long, head 14-25 ju broad, 

 wall thick, 3-6 ix, peripheral paraphyses thinner-walled and more 

 clavate. 



III. Telia amphigenous or only hypophyllous, scattered or 

 somewhat confluent, irregularly roundish, small, 0.2-0.4 mm. 



