INTRODUCTION 17 



most important agents in spreading them. Robins, for example, 

 devour great quantities of pulpy fruits like hawthorn berries, 

 grapes, strawberries, etc. The seeds pass through the body un- 

 digested, and indeed in many cases, better fitted for germina- 

 tion than before. Owing to their powers of flight, the seeds may 

 be discharged from the body many miles away from the parent 

 plant, and undoubtedly such fruit-eating birds have had much 

 to do with the rapid spread of many species. 



Another way in which birds may be agents in distributing seeds 

 and spores, is by means of mud in which seeds are imbedded. 

 Adhering to the feet of migratory birds the mud, with its cargo 

 of seeds, is thus carried long distances. 



Finally, man, involuntarily or otherwise, has been the cause of 

 the migration of many plants over pretty much the whole earth. 1 



Man and the Plant World 



Man's very existence is bound up with that of plants — whether 

 he is a naked savage maintaining a precarious existence by means 

 of the fruits, grains and roots he may find growing wild, or a highly 

 civilized white man, dependent on the grains, fruits and vegetables 

 that he has brought under cultivation. 



Most of the staple food plants of civilized man are so changed 

 by ages of cultivation that their origin is obscure; but some of 

 them, like rice and sugar-cane, are evidently closely related to 

 species still growing wild, and several species of wild bananas 

 are known, some of which are probably the ancestors of the culti- 

 vated varieties. So in northern countries, the common fruits, 

 apples, pears, cherries, plums, strawberries, etc., are evidently the 

 improved progeny of existing wild species. 



Wheat is supposed to have originated somewhere in Asia Minor, 

 maize in Mexico, while wild potatoes of several species are common 

 in parts of Chile and Peru. 



Having brought these plants under cultivation, man has carried 

 them with him in his wanderings, and thus has spread over the 

 whole earth. 



In addition to food plants, he had also developed many plants 

 for their fibres, such as cotton, flax and hemp. 



1 A recent noteworthy book on plant distribution is by Dr. J. C. Willis, Age 

 and Area; a Study in Plant Distribution and the Origin of Species, Cambridge, 1922, 



