44- THE PLANT WORLD. 



rootstocks, stolons and runners and thus increase their possessions 

 or find new homes. 



The various devices by which plants are shifted from place to 

 place is not merely to extend and multiply the species and reach a 

 fertile soil, but to enable them to flee from the great number of their 

 own kind, and their enemies among plants and parasitic plants. The 

 adventurers among plants often ineet with the best success, not be- 

 cause the seeds are larger or stronger or better, but because they find 

 for a time more congenial surroundings. Our weeds are good illus- 

 trations of this point. They are carried for long distances by man 

 and by him are planted in new ground that has been well prepared. 

 Every horticulturalist knows that apples grown in a new country, if 

 suitable for apples, are fair and healthy, but the scab and codling 

 moth and bitter rot and bark louse sooner or later arrive, each to be- 

 gin its peculiar mode of warfare. Peach trees in new places remote 

 from others are often easily grown and free from dangers, but soon 

 will arrive the yellows, borers, leaf curl, rot, and a number of other 

 enemies to cotnbat. For a few years plums are grown without danger 

 from curculio or rot or shothole fungus. It has long been known that 

 the surest way to grow a few cabbages, radishes, squashes, cucumbers 

 or potatoes is to plant them here and there in good soil at considerable 

 distances from where any have heretofore been grown. For a time 

 enemies do not find them. I have often noticed that while pear blight 

 decimated or swept off large portions of a pear orchard, a few isolated 

 trees scattered about the neighborhood — many neighborhoods — usu- 

 ally remain healthy. The virgin soil of the Dakotas produced at a 

 trifling expense healthy, clean wheat, but it was not long before the 

 Russian thistle, false flax and other pests followed to contest their 

 rights to the soil. If, as in endemic species, they seem for some rea- 

 son to be much restricted, they are very likely to becotne extinct and 

 give way to those not so restricted. Perhaps one reason why some 

 plants have become extinct or nearly so is their lack of means of mi- 

 gration. As animals starve out in certain seasons when food is 

 scarce, or, more likely, migrate to regions which can afford food, so 

 plants desert worn-out land and seek fresh fields. As animals retreat 

 to secluded and isolated spots to escape their enemies, so many plants 

 accomplish the same thing by finding the best places with some of 

 their seeds sown in many regions. Frequent rotations seem to be the 

 rule for many plants when left to themselves in a state of nature. 

 Confining to a permanent spot invites parasites and other enemies 

 and a depleted soil, while health and vigor are secured by frequent 

 migrations. 



