548 Rydberg : Rocky Mountain flora 



to think it a hybrid of the two species mentioned for the following 

 reasons. The form and the pubescence of the leaves are almost 

 exactly those of Carduiis acaulescens. The small and clustered 

 heads also suggest that species; but the plant has an evident stem 

 and the involucre is decidedly arachnoid-hairy. As C. scopu- 

 lorum and C. Parryi are the only species in Colorado which have 

 arachnoid involucres, one of these may be supposed to be the other 

 parent. As C. Parryi has also dilated erose bracts, it must be 

 thrown out of consideration. In C. crassus the involucral bracts 

 have also the long slender spines characteristic of C. scopidorum. 



Colorado: Sulphur Springs, Grand Co., July 17, 1905, Oster- 

 Jiout 3042. 



Neither of the two supposed parents is represented by speci- 

 mens from Sulphur Springs, but there is a specimen, Osterhout 

 361S, just cited above, which I regard as a hybrid of C. acaulescens 

 with another species. 



Carduus griseusXlaterifolius 



Carduus canalensis Osterhout, MS. 



This I included in Carduus griseus in my Flora of Colorado 

 but it differs in many respects from the type of that species, the 

 leaves being much broader and less lobed, the upper leaves with 

 broad auricles and the inner bracts with dilated erose tips. These 

 two characters suggest C. laterifolius, from which it dififers in the 

 long and broad spines of the outer bracts, characteristic of C. 

 erosus. 



Colorado: Canyon of Thompson River, Larimer County, 

 August 16, 1905, Osterhout joSq. 



This specimen was collected together with the type number of 

 C. laterifolius, viz., Osterhout jogo (the next number). 



Carduus griseus Xscopulorum 

 Carduus Osterhoutii Rydb. Bull. Torrey Club 32: 131. 1905. 



This has the habit, the leaf form, and the long flat spines of the 

 bracts of Carduus griseus, but the inflorescence is conspicuously 

 arachnoid-hairy as in C. scopulorum and the leaf segments are 

 rather more numerous than in C. griseus. The following speci- 

 mens belong here: 



