OF ARTS AND SCIENCES : JANUARY 26, 1870. 145 



Professor Lovering made a communication on the theory of 

 halos, and described the remarkable halo observed by him on 

 the afternoon of January 6th, inst. 



The President presented the following paper : — 



A Revision of the Eriog-onecs, by John Torrey and Asa Gray. 



This group was first put in order and characterized as a tribe of 

 Polygonucece by Mr. Bentham, in his monograph read to the Linnean 

 Society almost thirty-five years ago, and was re-elaborated by him 

 about eighteen years ago for the fourteenth volume of De Candolle's 

 Prodromus, which, however, was not published until the year 1856. 

 In the first monograph there were 40 species described under three 

 genera. In the Prodromus, where the group ranks as a sub-order, 105 

 species are described under seven genera. Including Lastarricea, which 

 Mr. Bentham did not recognize from its having no involucre, there 

 are 106 species and eight genera, — all the genera except the last, and 

 all the species but ten, being natives of North America. 



Being thus wholly American, mainly North American, and especially 

 characteristic of our drier Western regions, we are naturally interested 

 in these plants. To one of us they have long been a favorite study, as 

 the current botanical works, from the Account of the Collection made 

 by Dr. Edwin James in 1826, down to the fourteenth volume of the 

 Prodromus and the Botany of the Mexican Boundary, sufficiently show. 

 The other, the present writer, in the autumn of 1868 critically col- 

 lated his own collection (recently and specially enriched by most of 

 Nuttall's species, generously presented by Mr. Durand) with the her- 

 baria of Hooker and Bentham, now of the great collection at Kew, 

 and with Mr. Nuttall's proper herbarium, now belonging to the British 

 Museum ; and on his return he has, with his partner's specimens, 

 notes, and sketches to aid him, re-examined the whole, and embodied 

 the results in the present memoir. 



The genera here recognized are seven ; one of Bentham's (Mucronea) 

 being suppressed, and Lastarricea admitted. If the species are only 

 slightly increased, viz. from 105 to 115 (counting the omitted Chilian 

 Chorizant/tes), this is mainly due to the suppression of several of the 

 older species, especially in Eriogonum, which here amount to no more 

 than in the Prodromus, although 19 have actually been added. 



Clavis Generum. 

 1. Involucrum immutatum, fere semper calyciforme, raro nullum. 



(Folia integerrima.) .... Tribus I. EUERIOGONE^l. 



VOL. VIII. 19 



