16 PROCEEDINGS OF THE AMERICAN ACADEMY 



the light, when the spots appear as dark, black patches in the leaf 

 substance. 



5. D. Alismatis, (Nees), Cornu. 



On leaves of Alisma nutans and Plantago. 



Italy!, P^ ranee, Germany!, Finland!, England!; Siberia!; United 

 States ! . 



Subgenus II. Pseudodoassansia. 



Central portion of the sorus composed of an irregular-shaped mass 

 of fine, densely interwoven hyphce. Spores in several layers, loosely 

 compacted together. Cortex of large, well differentiated cells. 



6. D. obscura, sp. nov. Spot none. Sori in lines in the larger inter- 



cellular spaces at the base of the petioles and peduncles of the host, 

 globular to ellipsoidal, 180-220 /x by 200-300 /x, light brown. 

 Spores almost globular, 8-1 2 /a in diameter, light-colored. Cor- 

 tical cells obversely conical, conspicuously lobed at the outer, 

 broader end. Promycelium narrowly cylindrical, about 20 /* 

 long. Sporidia in whorls of 5 to 7, elongated fusiform, 16-17 jx 

 long and 1.5-2 /x. thick, producing bunches of secondary sporidia 

 without conjugation. 

 On petioles and peduncles of Sagittaria varinhllis. 

 United States ! (Cambridge, Mass. !, Medford, Mass. !, Norwich, 



Conn.!). 

 This species is very inconspicuous, being detected only upon the 

 most careful examination. When occurring upon the green portions 

 of the petioles and peduncles, it causes a very faint yellowish discolor- 

 ation. It most frequently inhabits the white portions at the very 

 base of these parts, and then the dark lines of sori show through the 

 more or less transparent outer tissues. It is abundantly distinct from 

 all the other species of the genus. The central hyphoe, the loosely 

 compacted spores, the obconic lobed cells of the cortex, and the method 

 of germination of the spores, are all characteristic. It seems to differ 

 so much from the species which cluster about D. Alismatis as to 

 demand a special subgenus for its reception. 



Subgenus III. Doassansiopsis. 



Sorus compact, not separating into its component elements at 

 maturity. Central portion consisting of a compact mass of pai'enchy- 

 matous tissue. Spores in a single layer. Cortex of small flattened 



cells. 



