August 14. 1895.] 



Garden and Forest. 



325 



ties. To the south-west, in Cochise County, its place is 

 taken by O. Bigelovii, a somewhat similar, but usually 

 much smaller, plant, which is also known under the name 

 Cholla. To the north and north-west it gives way to O. 

 Whipplei, which is the only cylindrical Opuntia found in 

 Arizona, to any great extent, on the Colorado plateau. To 

 the west, in Yuma County, it is no longer found, but in its 

 stead we find O. echinocarpa. 



Opuntia arborescens, a tree of much wider dissemina- 

 tion, and the small O. leptocanlis grow throughout the 

 entire country occupied by O. fulgida. O. arbuscula, O. 

 acanthocarpa. and occasionally large numbers of O. Bige- 

 lovii are found mingled with this plant north and im- 



Mountains and to the east, along the Mexican border, are 

 more broken and considerably higher than the Tucson 

 plains, which probably accounts for its presence there. It 

 grows in great numbers on the southern foot-hills of the 

 Santa Catalina Mountains, vi'hile a few miles farther south, 

 across the Rilitto River, on the open plains, are growing 

 the finest specimens of O. fulgida that I have ever seen. 

 Last fall I made an extended examination of these plants, 

 and traced all the variations to be found in a trip from the 

 plains into the foot-hills. Although the two forms appear 

 quite different in the different localities, where they inter- 

 mingle it is out of the question to separate them. The 

 flowers of both are of the same size, appear during July 



Fig. 46. — Opuntia fulgida in Arizona. — See page 32, 



mediately south of the Salt and Gila rivers, while in the 

 foot-hills and mountains throughout the south and central 

 portions of its range are found O. versicolor * and O. 

 mamillata. 



Opuntia mamillata is closely related to O. fulgida, and I 

 seriously question whether it is separable from it as a valid 

 species. It was described from material collected south of 

 the Baboquivari Mountains, in the direct range of O. ful- 

 gida, and in the original description the characters apply 

 almost equally as well to the latter species. The typical 

 O. mamillata grows on low mountains, foot-hills and 

 higher elevations than O. fulgida, which is characteristic 

 of the open plains. The plains south of the Baboquivari 



■"*= This is a manuscript name of Dr. Engelmann's, which was never publislied. 

 It represents a valid species growing in abundance on the low mountains of south- 

 ern Arizona. 



and August, and are the latest of the cylindrical Opuntias 

 to bloom. The petals of both are bright pink, fading to 

 purple ; few in number and strongly deflexed. The de- 

 flexion of the petals is a character, so far as I have 

 observed, common to but one other species of the cylin- 

 drical Opuntias found in Arizona — O. leptocaulis. t 



The fruit of th^plains plant is a little more spherical than 

 that common to the typical Opuntia mamillata, and the 

 tubercles are a little more prominent. These characters 

 are by no means constant and of no value in establishing 

 a specific distinction. In both the fruit is very proliferous, 

 does not ripen until the following spring, and frequently 



t In vol. vi.. Botany 0/ the Wheeler Survey, page \yT., it is stated that the flowers 

 of this plant, like those ol the restot the genus, are diurnal. So far as this plant in 

 Arizona is concerned, this statement is denied. 'I'he flowers open about four 

 o'clock in the afternoon and close shortly after sunrise the next morning. 



