208 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY 



THE PLANT IN RELATION TO ITS BIOLOGICAL 

 ENVIRONMENT. 



By Prof. J. B. Farmer, M.A., D.Sc, F.R.S. 



[Read July 14, 1914 ; Dr. D. H. Scott in the Chair.] 



Being the Twelfth " Masters Lecture." 



The vista of problems opened out by so comprehensive a title as that 

 of "The Plant in relation to its Biological Environment" is a very 

 long one. In the limited time at our disposal I propose to touch on 

 a very few of these problems, but I hope that we may gain some 

 idea of the way in which we may profitably attack them, and of the 

 general nature of the conclusions that are to be drawn from a closer 

 acquaintance with the problems themselves. 



The most obvious relations existing between any one plant and its 

 nearest neighbours perhaps is that of competition. Each successful 

 individual develops as fully as circumstances enable it to do, without 

 reference to, and often to the disadvantage of, the other members 

 of a plant community. This state of competition is especially severe 

 between the members of the same species, or between the individuals 

 of species physiologically related to each other. It is often, but not 

 always, less evident between species more remotely connected, though 

 it is perhaps never really absent altogether. But if one dips a little 

 below the surface of things, he soon comes to recognize that diversity 

 of specific affinity implies, and probably depends on, differences of 

 chemical nature, and the form of the problem thus assumes a 

 greater degree of precision, although it may not thereby lose any of 

 its complexity. 



A relatively simple and intelligible instance of the effects of com- 

 petition between nearly allied forms, physiologically speaking, is to be 

 seen in plants that inhabit areas where any of the essential nutritive 

 substances are either scarce or are only available at intervals. Plants 

 growing under these conditions are physiologically liable to starvation, 

 or at any rate they are exposed to periods of danger which prove fatal 

 to all that do not possess special means of meeting them. 



Desert plants afford an excellent example of what I mean. A 

 desert condition may be produced by permanent scarcity of water 

 with irregular rainfall, or it may be that the periods of scarcity are 

 only of periodical, though of long-enduring, occurrence. The vegeta- 

 tion of the latter regions is very different from that in which true 

 desert conditions prevail. In the real desert the persistent plants 

 are at no time crowded, but they often possess a great root system 



