Standley : Some Echinocerei of New Mexico 79 



The greatest difficulty encountered was the finding of some con- 

 stant character or group of characters by which to differentiate the 

 species. The extremes of variation of a given character upon any 

 single plant were farther apart than the means of the same char- 

 acter for two adjacent species. Neither was there any concurrent 

 variation of characters found. Instead, intergrading forms can 

 almost always be found between any two extremes of a given 

 character. E. poly acanthus, for instance, seems to possess forms 

 of spines that connect or lie midway between those of E. coccineus 

 and E. conoideus. Careful study was made of the arrangement of 

 the spines, color and shape of flowers, and stamens, and stigmas, in 

 the hope that some character would be found which would be con- 

 stant in one form, but no such peculiarity was found, with the pos- 

 sible exception of the spines. The curves showing graphically the 

 variation of separate characters, when compared, showed plainly 

 (i) the lack of concurrent variation, (2) the presence of intergrad- 

 ing forms, and (3) the overlapping of certain characteristics in the 

 selected lots of plants. The different distinguishable characters 

 were combined in almost every imaginable way upon the different 

 plants in the most bewildering manner. 



The best characters by which to separate the plants are probably 

 those of the spines, taking them as a whole. Their stoutness, length, 

 color, and arrangement furnish a means of distinguishing some of 

 the forms, although even this is far from being a satisfactory one. 

 In the plant which is our conception of E. coccineus the spines are 

 hght-colored, usually white or straw-colored ; they are compara- 

 bly short and slender. In E. conoidcus they are very long and 

 slender ; in most cases they are somewhat angled and more or less 

 deflexed ; their color is darker than in E. coccineus although it 

 varies considerably in different plants. In £. polyacanthus the 

 s P<nes are midway in length between those of E. coccineus and E. 

 conoideus, usually much longer than those of the former species 

 and frequently as long as those of the latter ; the spines are stouter 

 than those of the other two species, and are ordinarily terete, 

 rare ly somewhat angled near the base ; the color is quite variable, 

 ranging from almost white to dark-gray or almost black; the 

 spines, too, are more abundant, covering the plant more closely. 



lhe arrangement of the spines seems to be the same in all three 

 s Pecies. 



