SEED DISPERSAL 217 



examples are often met with. Most plants are distributed accord- 

 ing to natural ways by means of seeds, or the seedless plants 

 by spores (see Chapters XXV-XXXV). Some seedless plants, 

 however, are distributed also by buds (Lycopodium lucidulum, 

 paragraph 524, certain ferns as Cystopteris bulbifera, paragraph 

 511, footnote), and some by plant parts, and some seed plants are 

 distributed by other means than by seed. The best means, 

 however, for natural distribution of the seed plants is by the seed. 

 There are several natural means by which the seeds are dispersed, 

 the most important of which are as follows: first, by the wind; 

 second, by animals; third, by water; fourth, by mechanisms of 

 the fruits for the forcible expulsion of seeds. 



351. Dispersal of seeds by the wind. Many seeds which 

 are small and light are often blown by the winds for considerable 

 distances without having any special provision in the nature, of 

 floats or wings. The seeds of many grasses and other herbs are 

 very light and in strong gales are driven far, and when they fall on 

 rather hard loose ground may from time to time be driven along 

 just as particles of soil are. There are many seeds or fruits, 

 however, which are provided with special appendages which serve 

 as floats, or as surfaces, which "catch" the wind and enable them 

 to be borne along. Of the winged seeds notable examples are 

 seen in the samaras of the elm, where a thin membranous out- 

 growth attached to the seed renders the seeds buoyant, or the 

 wing is firmer as in the blades of the maple or pine. In the milk- 

 weed the flattened brown seeds are packed in great numbers and 

 very regularly in the large pods, and each seed has a large tuft 

 of long, white, delicate, hair-like outgrowths. These hairs are 

 packed very closely together in the pod. As the pods split open 

 the hairs become dry, and in curling take up much more room, 

 thus crowding the seeds out of the capsule, when they are caught 

 by the wind and floated away. To show how buoyant they are, 

 such seeds may be set free in the quiet air of a room, and they 

 will float slowly to the floor. In the Virginia creeper, or virgin's 

 bower, the long curved style remains attached to the akene and 

 is covered with numerous delicate bristles. The style when dry is 



