638 General and Applied Biology 



beautiful elm trees and by so doing could have saved large quantities of 

 money. The destruction of large numbers of elms is not only a direct 

 loss, but their absence also affects the ecologic relationships of other 

 plants and animals which are present in the area in which they are 

 destroyed. If there were no quarantine and everybody were permitted 

 to import all types of vegetation, many detrimental, diseased, and para- 

 sitic plants as well as parasitized plants, would quickly make their ap- 

 pearance in this country. This would greatly add to our already enor- 

 mous problems of economic botany. 



(b) Transportation of Animals and Plants by Automobiles, Trains, 

 Ships, and Airplanes: Only a little time need be spent on the highways 

 or wharves to see how animals and plants are easily transported long 

 distances by any of a number of methods. Not only are these truly 

 methods of dispersal, but after animals or plants have been suddenly 

 imported into new regions, their presence quite decidedly influences 

 the former population to such an extent that an entirely new ecologic 

 relationship will exist. These methods of dispersal are man's inventions 

 and an animal or the seeds of plants may be quickly transported a 

 great distance in a short time. 



(c) Usefulness and Domestication of Animals and Plants: The very 

 rapid changes in natural vegetation due to man's activities undoubtedly 

 influence the distribution of numerous animals dependent on or asso- 

 ciated with a vegetation of that type. The clearing of a land of its 

 trees has a decided effect on the animal population of that area. The 

 introduction of new species of wild or domesticated plants also directly 

 or indirectly affects the animal distribution within that area. Man not 

 only has taken domestic animals with him as he has gone over the 

 earth's surface, but these animals also have taken their parasites with 

 them. This has resulted in a necessary redistribution of the population 

 into which the newcomers were taken. In general, it may be concluded 

 that what may appear to be a small, insignificant factor may in the 

 end prove to be a very influential one as far as ecology is concerned. 

 The destruction of a few apparently useless animals may have a great 

 effect in nature's balance, just as the introduction of a few apparently 

 harmless varieties may cause an ecologic readjustment. 



Domestication of useful plants has resulted in their being protected 

 and cultivated, and hence their wide distribution has been ensured. 

 The cultivation of domestic plants has a tendency to influence many 



