318 NATURE SKETCHES IN TEMPERATE AMERICA 



the source and dispersal of species. There are many observed 

 ways by which plants and animals are disseminated. For 

 instance, in plants, the wind is perhaps the most important 

 means of scattering seeds and fruits. Examples of this method 

 are shown in the winged fruit of the maple, and the fluffy 

 seeds of the milkweed and thistle. Water, also, has been another 

 factor of great importance, as well as snow and the wind 

 combined. 



Animals aid the dispersal of fruits and seeds by eating the 

 fleshy, edible kinds, such as the cherry, bittersweet, raspberry, 

 and the poison ivy; the undigested seeds being dropped in the 

 excreta. There are also explosive fruits and seeds that possess 

 a peculiar mechanism for shooting the seeds some distance 

 away from the place of growth, while still others are provided 

 with creeping mechanisms. Lastly, man has inadvertently 

 scattered many weed species which were contained In adulterated 

 clover and other crop seed. Free-moving animals, through 

 migration, become widely dispersed, the wind here, hs in the 

 case of seeds, aiding them in these movements into new fields. 

 Young moUusks which frequent ponds are often carried on the 

 feet of water birds and thereby transported to new and similar 

 habitats where they may start a new colony. 



Habitats of Plants and Animals 



Merrlam and Allen, as well as others, believe that defin- 

 able life zones are apparent over different regions of North 

 America. The dependencies upon the habitat of free-moving 

 animals, however, are not often clearly perceptible. These 

 relations of the environment are generally not so evident, for 

 instance, as the physical effect that water or light exerts upon 

 fixed plants. But in some special cases they are quite marked. 

 The physiographic features in the landscape doubtless have a 

 great deal to do with determining the habitat of animals and 

 plants. The real habitat of an animal is determined by the 

 place in which It habitually breeds.' 



Woodworth,^ in an article on "The Relation between Base 



' See classified habitats at the end of this book. 

 " American Geohgist, XIV, 1894!. 



