SECTION I 

 INJURIES INDUCED BY PLANTS 



THIS is not the place to discuss the many conditions brought 

 about by the struggle for existence for space, food-materials, 

 water, and light between plants of the same or opposite species. 

 Any plant may prove injurious to another if it makes the same 

 or similar claims on the constituents of the soil. When two 

 plants compete with each other, success does not alone depend 

 upon the rapid rate of growth of any particular species on a 

 given situation, but is determined largely by the rate of growth 

 which characterises individual plants ; and it is this which is 

 mainly decisive in pure woods. It has long been known that 

 superior individual growth manifests itself in the earliest stages 

 of the life of a tree ; in fact, sometimes for instance, in the 

 case of the oak it is recognizable in the size of the fruit. 1 

 It is therefore of the greatest importance not only to exer- 

 cise care in the selection of the seed, but also to remove 

 weak plants when transplanting in the nursery. When 

 crowded, all plants must struggle with their nearest neigh- 

 bours ; but I do not consider that it is the province of vegetable 

 pathology to discuss these conditions : rather do I hold that 

 I should closely confine myself to the consideration of those 

 injuries which consist in the direct attack of one plant on 

 the life and health of another. 



1 Th. Hartig established this fact experimentally in the nursery at 

 Brunswick thirty years ago. 



