37 2 ECOLOGY. 



678. The milkweed, or silkweed. — The common milkweed, or silkweed 

 (Asclepias cornuti), so abundant in rich grounds, is attractive not only 



Fig- 474- 

 Milkweed (Asclepias cornuti) ; dissemination of seed. 



because of the peculiar pendent flower clusters, but also for the beautiful 

 floats with which it sends its seeds skyward, during a puff of wind, to finally 

 lodge on the earth. 



679. The large boat-shaped, tapering pods, in late autumn, are packed 

 with oval, flattened, brownish seeds, which overlap each other in rows like 

 shingles on a roof. These make a pretty picture as the pod in drying splits 

 along the suture on the convex side, and exposes them to view. The silky 

 tufts of numerous long, delicate white hairs on the inner end of each seed, 

 in drying, bristle out, and thus lift the seeds out of their enclosure, where 

 they are lifted like fairy balloons, buoy?nt as vapor, they go bearing the 

 precious burden of an embryo plant, which is to take its place as a contest- 

 ant in the battle for existence. 



680. The virgin's bower. — The virgin's bower (Clematis virginiana), too, 

 clambering over fence and shrub, makes a show of having transformed its 



