398 PROCEEDINGS OF THE AMERICAN ACADEMY. 



spores possessing the thinnest walls. As I have stated, thick-walled 

 spores are rarely to be seen in the young sori ; but they are more 

 abundant with the increasing age of the sorus, and the best defined of 

 this type are always found unattached. These spores have orange- 

 colored contents in the fresh condition. They are more or less oval 

 in outline, with from four to eight germ pores generally indefinitely 

 distributed over the surface, as in Figures 4, 8, and 10, taken from 

 dried material. In every sorus showing both kinds of spoi'es it needed 

 little search to find connecting stages of every grade between the 

 irregularly elliptical thin-walled spores and the oval or polygonal thick- 

 walled spores. The cell wall is found in different degrees of thickness, 

 and the number of well defined germ pores manifestly increases in 

 proportion to this thickness of wall. Then from these results we de- 

 rive the necessary conclusion that the thin-walled spores are merely the 

 immature condition of the thick-walled mature uredo form. 



The herbarium material utilized in this study represented a number 

 of host-plants, and the collections were made in widely separated 

 localities ; the diversity of material, therefore, should give a broad 

 basis for reaching definite results. I have examined Uredo Aspidiotus 

 Pk. on Phegopteris Dryopteris, Myc. Univ. 9oO, the material from 

 the author of that species; also Uredo Pulypodii (Pers.) DC. on the 

 same host from Krieger, Fung. Sax. 566, Syd. Ured. 746, and a speci- 

 men collected by Dr. Farlow at Shelburne, N. H. I have studied 

 specimens on Oystopteris fra gills bearing names as follows : Uredo 

 Polypodii (Pers.) DC, Krieger, Fung. Sax. 567, and Uredo Flllcum 

 Desm., Erbario Critt. Italiano, 889 ; also material from Switzerland col- 

 lected by P. INIagnus and by Winter, and from Granville, Mass., Manitou, 

 Col., Oregon, Gorham, N. H., and from near Boston, Mass. Other her- 

 barium material included a specimen on Phegopteris Dryopteris from 

 Thumen, Franconia, Germany; and Uredo Polypodii (Pers.) DC. on 

 Pulypodium Dryopteris, Eriksson, Fung. Paras. Scand., 70 b. I must 

 admit that with the examination of only a few preparations of herba- 

 rium material I might be inclined to agree with previous writers in 

 distinguishing two distinct kinds of uredospores, but the fresh material 

 showed beyond doubt that the two forms are but different phases in 

 the development. Likewise, this process of development was traced 

 in all of the herbarium specimens above enumerated. Figures 1 to 8 

 inclusive show two series in which this development may be traced. 



In view of Dietel's mention of the four germ pores equatorially 

 disposed in the thin-walled spores, it was thought well to study this 

 further ; hence young sori were isolated, the spores cleared and stained. 



