VALl'E OF TACTI AS FOOD FOR STOCK. 15 



COMMON AND SCIENTIFIC NAMES. 



Considerable attention has been g:iven to the popular names by 

 which the various species are designated, especially the larger Mexican 

 forms, but inasmuch as these are to be more fully considered in 

 another publication now in process of preparation a full discussion of 

 the subject is postj)oned. 



The chaotic condition of the scientihc literature and the general 

 unperfection of knowledge of prickly-pear forms have rendered it very 

 difhcult to properly name the species discussed. The purpose of the 

 A\Titers has been to present the exact status of their information, 

 indicating a doubt wherever one occurs. The Engelmann species, 

 which arc largely I'nited States forms, are comparatively easily deter- 

 mined, in most cases through a reference to the types in the herbarium 

 of the Missouri Botanical Garden. In case of long-established species, 

 however, it is absolutely impossible to correlate the specimens with the 

 literature and deternnne what name belongs to the plant under dis- 

 cussion. (Jjnintia tuna, for instance, has been paraded in literature a 

 great deal, and to it has been assigned all sorts of species; but, as 

 pointed out b}^ Berger and Maiden especially, no one knows what the 

 species is, and the writers know of no way by which its identity can 

 ever be determined. 



Some species are referred to their proper genera only. Others 

 are given common names besides, but the majority of them are given 

 scientific names. All species receiving chemical analyses are repre- 

 sented in our collections by specimens mounted upon sheets in the 

 ordinar^^ way or put up in boxes or in liquid. Many are growling 

 in conservatories or upon one of the plantations maintained by the 

 United States Department of Agriculture, while the seeds of many 

 species have been widely distributed to those interested in the scien- 

 tific and economic study of the group. The work is therefore well 

 supported by specimens to which access will be had in completing in 

 the future such naming as has not liitherto been undertaken. It was 

 early recognized that good drj- specimens were absolutely necessary 

 for this work in order to make the chemical analyses and determi- 

 nations of permanent value. 



Whenever a sample or set of samples represents a striking or con- 

 stant variation it is treated separately in the text; consequently 

 Opuntia lincnieimeri, for instance, appears several times under two or 

 more headings. Each number or group of numbers is accompanied 

 by a brief set of notes made in the field beside the plant when the sam- 

 ples were collected, elaborated and perfected by subsec^uent experience. 

 These are presented as field notes simply and not as full technical 

 descriptions. This rather fidl set of notes, popular and scientific 

 names, and, as a final resort, our specimens and photographs, w^ill 

 make it possible to easily verify the determinations of the writers. 



4359— No. 102—07 2 



