202 ECOLOGY 



interests, and the results to ecology are not great. The field here 

 opened is boundless. 



It is one of the chief difficulties of the ecologist measuring the effects 

 of the different forces of nature upon plant life, that they are all acting 

 at once. Each plant when in a state of nature is simultaneously 

 affected by the physical and chemical nature of the soil, amount of 

 light, degree of moisture, exposure to wind, density and purity of the 

 air, crowding of other plants, and attacks of animals. Its develop- 

 ment is the mathematical resultant of the composition of these forces. 

 To understand their relative influence upon the plant it is necessary 

 to isolate them. To do this it is only needful to vary one influence 

 while maintaining the stability of the others. Such experiments 

 require no great ingenuity, and may even be applied to plant com- 

 munities of some size; thus the addition of a single chemical substance 

 to the soil, changing the amount or character of the light-, adding or 

 withdrawing competing plants, modifying the degree of moisture 

 in air or soil, or controlling in some single regard the animal environ- 

 ment, are nearly always possible, and often very easy experiments. 



It may be said that these things have all been done repeatedly by 

 the plant physiologist. This is very true, but it is to be remembered 

 that his point of view has been different. He has tried these experi- 

 ments to learn the specific reaction upon the particular plant. To the 

 ecologist, however, their interest would be in the comparative effect 

 upon the different components of a flora, for it would be thus that he 

 would gain new insight into the fundamental factors in distribution. 



Professor Warming, a great leader in ecological investigation, said 

 some years ago, "There is scarcely a more attractive biological field 

 than to determine what the weapons are with which plants force one 

 another from their positions." Professor Ganong, in recently com- 

 menting upon this idea, says, "To-day we know no more of that sub- 

 ject than when Warming wrote those words." May not this problem 

 be simplified by reversing it? Would it not be better to begin not 

 with the weapons, .but with the vulnerability of plants? Is it not 

 safe to assume that when certain plants give way in competition it 

 is because they are to a greater extent subject to some one or more 

 adverse influences? The nature of these and the degree to which each 

 species of a community is affected by them can to a great extent be 

 determined by experiments such as have been suggested. When the 

 relative vulnerability of the different plants has been found, it may 

 be logically assumed that the weapons of the more resistant are 

 nothing other than their superior faculties of withstanding these 

 untoward influences, forces which by artificial control may be ascer- 

 tained with definiteness and measured with precision. 



To this point I have spoken chiefly of the development of ecology 

 as a pure science. Although we live in an age when the pursuit of 



