THE BATTLE OF LIFE' AMONG PLANTS. 81 



Again, root-excretions (assuming their existence) cannot be produc- 

 tive of injury, as we are assured by Dr. Gilbert that clover has been 

 grown in the same plot of garden-soil at Rothamsted for eighteen 

 years in succession, while only a few hundred yards off no condition 

 of manuring has hitherto been successful in restoring the clover-yield- 

 ing capabilities of the land. 1 Reverting, however, to the alleged an- 

 tipathies of one plant to another, we may make passing mention of the 

 eurious circumstance recorded by M. Paul Levi, 8 that the lianas or 

 climbing plants of the forests of Central America have their likes and 

 dislikes, and that they will not attach themselves to particular trees 

 even when brought into juxtaposition with them. It is significent 

 that the trees which are thus slighted by the twiners are just such as 

 are ill-adapted for the support of such plants, being such as have tall, 

 unbranched trunks, with smooth bark and a dense, overhanging, dome- 

 like canopy of foliage. It is not only the climbing plants that refuse 

 to grow on such trees, but to a less extent, also, the mosses, ferns, 

 orchids, Bromeliads, and other epiphytal plants. 



It is obvious, from what has been previously said, that human in- 

 terference affects these internecine conflicts of plants very materially. 

 It is clear also that the cultivator can very often avail himself of them 

 to his own profit. From this point of view the experiments and 

 observations carried on at Rothamsted by Mr. Lawes and Dr. Gilbert 

 are most important, especially those relating to the struggle among 

 pasture-plants, and the circumstances favoring certain plants more 

 than their fellows. No detailed report of these particular experiments 

 has hitherto been published, and only a few scattered notices in the 

 Proceedings of the Horticultural Society (June 2, 1868) have appeared 

 concerning them. We can, however, give some idea of their scope 

 and nature by stating that a part of the park at Rothamsted, which 

 has been under grass for centuries, has been divided into plots of 

 equal size, placed side by side under conditions as nearly equal as 

 possible. Some of these plots have been left unmanured ; others, 

 some twenty in number, have, for the last ten or twelve years, been 

 subjected to various manures, the constitution and proportions of 

 which are accurately determined. The general herbage of the park, 

 like that of the unmanured plots, consists of some fifty species of 

 plants, including sundry grasses, clovers, docks, umbellifers and other 

 plants commonly found in such situations. In the several manured 

 plots a change is observable, sometimes slight, at other times vast, 

 and the change does not show itself so much in the superior luxuri- 

 ance of any one plant, or in the starved condition of another, as it does 

 in the more or less complete exclusion of certain plants, and in their 

 replacement by others. Thus, while the unmanured plots contain, 

 say, fifty species of plants, others comprise less than half that num- 



1 Journal of the Horticultural Society. New Series, vol. iii., p. 91. 



2 Cited in the Gardener's Chronicle, 1870, p. 383. 



vol. in. 6 



