202 MISSOURI BOTANICAL GARDEN. 



increases in size as one passes into Arizona, where it 

 becomes a rather large tree, but of far simpler habit than 

 brevifolia, and much smaller than the larger plants of that 

 species. Its underground axis is of the glauca type, — 

 long, tough and branched,*— so that it is difficult to remove 

 oven the very small plants from the ground. The inflo- 

 rescence appears to be terminal, so that the crown which 

 has bloomed has its apical growth destroyed ; but a lateral 

 bud develops into a new crown, and in time a number of 

 thick new heads may form in this manner, making a pluri- 

 capitate plant. The shortness of these branches, and their 

 dense covering of long spreading leaves, contrasted with 

 the frequent slendernesss of the trunk, after its lower leaves 

 have become reflexed and dry, gives the tree a peculiar and 

 not ungraceful appearance, quite different from that of 

 any other species native of the United States. The old 

 flower stalks, when above the reach of cattle, usually hold 

 their dehiscent capsules for at least a year, and at length 

 break away without disarticulation above the base, which 

 persists for years along the side of the stem, closely applied 

 to it because of the erect sympodial habit of the latter. 



At Eagle Flat, Texas, I was able to spend several even- 

 ings about the first of June in studying the pollination of 

 this species, which there rarely becomes six feet high and 

 begins to bloom when not more than two feet high, so that 

 observations are more readily made than on the taller 

 plants of southern Arizona. 



The flowers are nearly pure white, with quite acute thin 

 petals, and conform in most respects to those of glauca. 

 The style, however, is white, as in rupicola and filamen- 

 tosa, and its segments are little thickened dorsally. The 

 septal nectar glands are very well developed, as in all of 

 this group, and reach to the base of the ovary. They ap- 

 pear to be slightly more active than in related species, for 

 a little nectar was recognized in several flowers, and two 



* Engelmann, Coll. Writings, 279, 280. 



