22 RUBBER-CONTENT OF NORTH AMERICAN PLANTS. 



The several series of analyses of different parts of the same plant 

 indicate conclusively that the percentage increases up the stem until 

 the young tips are reached, when it again falls off in some cases. The 

 continued increase, even to the uppermost sections, as reported under 

 a few numbers, may be due to a different selection of the height at which 

 the cuts were made. For a comparison between different plants it would 

 be better to take equal portions of all parts above the woody base. 



ASCLEPIAS SULLIVANTI. 



Description. — Plant a stout, strictly erect perennial herb, 2 to 5 

 feet high; roots connected by underground branches, which give rise 

 to clumps of stems at irregular intervals, but 1 to 3 feet are common 

 distances between the clumps; stems sometimes solitary, but usually 

 2 to 6 from the base, simple or with few branches, straight, very smooth 

 and without hairs; leaves numerous to the top, 7 to 12 pairs on each 

 stem, sometimes 3 or 4 in a whorl at some of the joints, oblong or some- 

 what ovate, 4 to 6 inches long, 1.5 to 3 inches wide, thick, smooth, not 

 hairy; flowers purplish or flesh-colored, appearing from the middle of 

 June to early September, many in a spherical stalked cluster (umbel) 

 which terminates the stem, or the clusters sometimes also in the axils 

 of the upper leaves; pods on curved stalks, erect, ovoid, 3 to 5 inches 

 long, about 1 inch thick, not hairy, but usually with small blunt proc- 

 esses near the apex, maturing in late August and September. 



References.— GTB.y, Syn. Fl., 21; 91, 1878. Britton and Brown, III. Fl., ed. 2:27, fig 

 3390, 1913. 



Distribution and ecology. — The range of this species is from southern 

 Ontario and Ohio to Kansas, Nebraska, and Minnesota. While it 

 may be expected almost anywhere throughout this section where soil 

 and moisture conditions are suitable, there are but few records of its 

 occurrence in abundance. Professor T. J. Fitzpatrick, of the Univer- 

 sity of Nebraska, reports it as common on many of the bottom lands 

 along streams in southern Iowa, and especially along the Chariton 

 River opposite Centerville. Other localities where it may be obtained 

 include Lincoln, Nebraska; Manhattan, Kansas; Baltimore and Ohio 

 Railway near Kimball, Erie County, Ohio. 



Asclepias sullivanti grows only on low land where the soil is moist. 

 At the present time it seems to be most abundant along streams and 

 lake-shores, where the land is overflowed at certain seasons, but this 

 must not be taken as evidence that such conditions are essential to its 

 growth. Possibly it was once much more common on better drained 

 and drier soil, from which it has been crowded by agricultural practice. 

 Its distribution indicates that it can endure very low temperatures in 

 winter, at least as low as30° F. below zero, and that a fairly high summer 

 temperature and humidity are at least suitable and perhaps requisite 

 to its best development. 



