6 BULLETIN 800, TJ. S. DEPAKTMEE'T OF AGRICULTURE. 



A, subvertidllata. In our opinion there is only one species of this type in New 

 Mexico. 



The study of fresh specimens in New Mexico, Colorado, Utah, and 

 the examination of dried specimens in the herbaria leads to the con- 

 clusion that A. vertlcillata does not occur in the Kocky Mountain 

 country, but is a species of the Atlantic Plains and the Mississippi 

 Valley. 



A, mexicana grows from 3 to 5 feet high, and has wider leaves and 

 shorter horns than other species of the whorled-milkweed group. It 

 ranges from southern Mexico through western Arizona, California, 

 and western Nevada to the Columbia and Snake River valleys in 

 Washington and eastern Idaho. 



A. pwnila {A. "vertlcillata var. fwmilGb) is a low, tufted plant with 

 leaves irregularly crowded on the stem. The plant, if it proves to be 

 only a variety, belongs with A. galioides. It ranges from South Da- 

 kota to Co]x)rado, western Nebraska, and New Mexico. 



A. galioides was included by Dr. Gray in A. verticillata. Recent 

 authors have tried to distinguish the two species by the shape of their 

 hoods, describing those of A. verticillata as entire from a rear view, 

 and those of A. galioides as hastate-sagittate. 



All the whorled-milkweed flowers seen in the summer of 1918 had 

 entire hoods. Examination of these specimens after drying shows the 

 hoods hastate-sagittate. A study of herbarium specimens indicates 

 that hoods of both A. verticillata and A. galioides are often hastate- 

 sagittate when dried. These species, however, differ in two respects. 

 A. verticillata has a Bunch of long, fibrous roots and smooth pods; 

 A. galioides has horizontal main roots and hairy pods, and in these 

 characters agrees with A. 'pumila and A. nvexicana. In flower the 

 species appear to be nearly identical. 



There appears to be no doubt that the plant which has been respon- 

 sible for the cases of poisoning in Colorado, Utah, Arizona, and New 

 Mexico is A. gaUoides. 



DISTKIBUTION AND HABITS OF THE PLANT. 



The plant ranges northward from Central America through Ari- 

 zona and New Mexico to central Utah and central Colorado. 



It has been found in Utah as far north as Beaver County (pccord- 

 ing to Esplin) and the foothills of the Uinta Mountains (according 

 to Jones). In western Colorado it has been seen on Grand River as 

 far up as Glenwood Springs, on the North Fork of the Gunnison 

 River as far as Bowie, and on the Gunnison River to the Black 

 Canyon. 



In eastern Colorado it has not been observed north of the Arkansas 

 watershed, but occurs on that river as far as Parkdale, just above 

 the Royal Gorge. Figure 1 shows, in a general way, its distribution. 



