110 MASSACHUSETTS HORTICULTURAL SOCIETY. 



exterminated, and hence produce no lasting effect upon plant distri- 

 bution. Such is the case with grains and most European garden 

 flowers introduced into this country, which rapidh' die out as soon 

 as cultivation ceases. Cultivation largely consists in keeping away 

 from a plant its natural enemies ; and most plants when carried la 

 a new home cannot, unaided, compete with the native forms, Avhose 

 constitutions have been acclimatized by centuries of residence. 

 Hence the transfer from place to place by man, however extensive 

 it may be, of plants which could not exist in the new region with- 

 out his constant care, has but little to do with our present subject. 

 But there are some plants which he transfers, generally unintention- 

 ally, which often find in their new homes conditions favorable to 

 their rapid growth and spread ; and they frequently make them- 

 selves at home to such an extent that they become great nuisances. 

 Such are most of our weeds. As is well known, nearly every 

 troublesopie weed in our own regions, for instance, has been intro- 

 duced either from Europe or from the open lands of the West. 

 The reason for this appears to lie in the direction pointed out 

 by our greatest botanical philosopher, the late Asa Graj'. The 

 native weeds are all forms which have developed in or with the 

 woods, and when the latter were removed in the processes of 

 cultivation, the}' found conditions to which the}' were unaccus- 

 tomed and for which their constitutions were but poorly fitted. 

 The European accidentally introduced forms, however, after their 

 centuries of struggle with European civilization, hardy and self- 

 reliant as our own street urchins, found here a field not only 

 just such as they were adapted to, but occupied by no forms which 

 could offer them vigorous competition. Hence, they multiplied 

 and occupied the earth. In a lesser degree the conditions were 

 favorable to plants from the west accustomed to open ground. It 

 is along these lines that man has produced his greatest effects 

 upon plant distribution. You notice that we are considering now 

 the question from the Naturalist's stand-point, not from the Horti- 

 culturist's. To the latter the transfer of Cinchona from South 

 America to India, of Eucalyptus from Australia to California, of 

 the Maize to Europe and China, is a large matter in comparison 

 with his accidental transfer of a few troublesome or ugly weeds 

 from the old world to the new ; but to the naturalist the question 

 of the weeds is of as much if not more interest and importance, — 

 certainly it is to the organic world which the naturalist ought 

 honestly to study. 



