DISSEMINATION OF SEEDS. 129 



"The wing and coma of seeds are functionally identical 

 with the wing of the samara and with the pappus of the 

 pericarp in the achenes of the Composite, but morpho- 

 logically are unlike them." 



Tilia Americana, the linden-tree, has a somewhat pecu- 

 liar mode of dispersing its seeds. Its flowers appear in 

 clusters in the upper axil of a leaf, the stem of each 

 cluster being attached for about half its length to a 

 ribbon-like bract of about the length of the stem. The 

 fruit, which is a round nut of about the size of a pea, 

 remains attached by the stem of the flower-cluster to the 

 bract before-mentioned. As this falls from the tree the 

 bract, moved by the wind, spins around and travels quite 

 a distance. When, as is often the case, the tree stands 

 on the shore of a pond or river, the seeds fall upon the 

 surface of the water and the winged appendage, acting as 

 a sail, wafts the seeds to various points on the opposite 

 shore. 



The structure of the pericarp in some fruits is such 

 that by means of it they are wafted to a distance. This 

 is true of Stapkylea trifolia, Oolutea arborescens, and 

 Cardiosjjermiwi halicacabum, which last from its inflated 

 capsule is called the balloon-vine. The inflated seed- 

 vessels of these plants seem intended for the purpose of 

 wafting the seeds by exposing to the wind a large, light 

 body. 



Many plants not possessing any of the before-mentioned 

 peculiarities are carried off bodily by the wind to distant 

 localities. "The rose of Jericho," Auastatica hierocliun- 

 tica, one of the Cruciferaa, has this method of dissem- 

 ination. Its short stem separates into long, spreading 

 branches ; its leaves are obovate ; its flowers are small, 

 white, sessile, and are succeeded by pods which begin to 

 ripen on the approach of dry weather ; the branches 



