OF THE UNITED STATES. 25 



with a number of holes, usually from five to ten, and it is through these holes that the ger- 

 minal tubes protrude. Keess considers that the number of pores can be used as a means of 

 distinguishing species, but my experience shows that the number is variable in the same 

 species. The spermogonia are small and found in clusters in discolored spots on the 

 upper surface of the leaves, where they are seen as brownish black dots. The spermatid 

 are punctiform and are almost identical in all the species of the genus. 



The Roesteliae are very abundant on the leaves of our different thorns and fruit trees, 

 and they are also found on the fruit. In some cases they cause distortions of the stems, 

 which swell to twice their original size and become cracked and very irregular, or, if the 

 stems attacked are small and flexible they often become much recurved. The presence of 

 members of this genus in the leaves is indicated by j^ellowish or reddish sj^ots in which 

 the spermogonia appear first on the upper surface, while the aecidia do not become visible 

 until after a considerable interval in most cases. The amount of swelling produced in the 

 leaves by the aecidia varies much in the different species. In some it is only slight, 

 often in the form of a ring, but in others prominent ovoid or conical projections are found. 

 The duration of the mycelium is a point of importance in considering the connection be- 

 tween Roestelia and Gymnosporanguim. Certainly in some cases it seems to be perennial, 

 but supposing that there is a genetic connection between the two genera just named, one 

 would expect the Roesteliae to be annual products of the germinating sporidia of the differ- 

 ent Gymnosporangia. The date of the appearance of the different species is also of import- 

 ance in attempting to connect any particular Roestelia with a given species of Gymnospo- 

 rangium. Some species, as R. j)enicillata, mature in May and June, almost simultaneously 

 with the Gymnosporangia, while other species, as R. hotryapltes, do not ripen until the 

 middle of September or October. From an economical point of view, the Roesteliae 

 are of considerable importance, since they attack the leaves of so many of our fruit trees, 

 causing them to fall prematurely, and some of the species attack the yonng fruit as well 

 as the leaves. 



The determination of the species from their anatomical structure is attended with many 

 difficulties. The principal characters used are the gross appearance of the spots and swell- 

 ings and the microscopic characters of the spores and the cells of the peridium. Too 

 many species depend upon the amount of splitting of the peridium which evidently must 

 depend to a large extent upon the age of the latter and accidental circumstances. The 

 species of Roestelia are, moreover, not limited to a single host-plant, and one must nat- 

 urally expect modifications of the swellings and of the peridium according as the Roestelia 

 is parasitic on different hosts. 



Roestelia botrtapites Schw. 



Caeoma (Roestelia) hotryapites Schweinitz, Syn. Fung. Am. Bor., No. 2902. 



Roestelia Ellis'u Peck, Bull. Torrey Club, Vol. vii, p. 13. Exsicc. Mycoth. Univers., No. 



431. 

 Roestelia hotryapites Schw., Berkeley in Grevillea, Vol. v, p. 34; Farlow, Bull. Bussey 



Inst., Vol. II, p. 225. 



Aecidia hypophyllous, borne in tuberculated or pyriform protuberances about an eighth 

 of an inch high, sometimes solitary, usually densely aggregated or consolidated, 8-14, 



