OP ARTS AND SCIENCES. 265 



Such, in brief, were the results reached, and at first sight it would 

 seem an easy matter, having obtained aecidia from five of the seven 

 species of Gymnosporangium, to refer these, at least, to their respective 

 RcesteUce. The task is, however, not so simple, for the reason that 

 considerable confusion exists as to the identity and distinctions of the 

 species of Rcestelia as they occur in nature. 



Of the forms resulting from the present cultures R. aurantiaca and 

 botryapites are unmistakable, and cannot be confounded with any 

 other New England form, as may be said also of R. transformans. 

 With the others, unfortunately, the case is different. Even with ma- 

 terial collected out of doors it is difficult satisfactorily to separate them, 

 either by gross appearance or microscopic characters ; while a detailed 

 examination of each species, as at present defined, is very confusing, 

 and leads lo the conclusion that the usual characterization of these 

 species is erroneous in several respects. 



The form, for instance, generally known in this country as R. peni- 

 cillata, occurring on Pyrus coronaria and P. inalus, as well as upon 

 Cydonia vulgaris and perhaps Cratcegus, described by Schweinitz as 

 ^cidiiim pyratum, appears to have been incorrectly referred to the 

 first-mentioned species. The European form distributed as R.penicil- 

 lata on Pyrus mains and Cratcegiis, and considered by some authorities 

 as a form of R. lacerata, seems to be very properly retained by Winter 

 as distinct, under the name ^cldium penicillatum, and an examination 

 of four exsiccati, (Karst. Fung. Fennine 295, Rabh. Herb. Myc. 788, 

 Rabh. Funo;. Eur. 1390, Erickson Fung. Scand. 75,) together with 

 specimens from the Tyrol in Prof. Farlow's herbarium, indicates a 

 well-marked species quite distinct from any American form known to 

 me. The spores are as large as those of aurantiaca, averaging about 

 40 fx in diameter, while the peridial cells are very characteristic. Not 

 only are they very large (about 120 X 65 /x), but the markings are 

 peculiar, and consist of fine, clearly marked branching and anastomosing 

 strioe running transversely without prominent ridges. In our form, 

 on the other hand, the spores are smaller, about 25 /a in diameter, 

 while the peridial cells are smaller and narrower, their average meas- 

 urement being about 22 X 80 [x, and are marked by strite running 

 obliquely and anastomosing obscurely, the outline of the cell being 

 broken by coarse ridges. In both species, the cells when isolated tend 

 to become curved outwards, most conspicuously so in the American 

 form ; a fact to which is dile the outward curling of the peridial lacera- 

 tions resulting in the habit peculiar to both. 



Turning next to R. lacerata, there seems to have been a confusion 



