40 THE AMERICAN BOTANIST 



dominated by a live and let-live policy. Their habits of life 

 are such as not to interfere with one another, while the nature 

 of the habitat is such that other species cannot come in and 



start trouble. 



The protection afforded many species of plants by their 

 habitat is a subject that usually does not receive the amount of 

 attention from plant students that its importance warrants. In 

 some instances as in sand-barrens, there is room for many 

 more plants than occur. The plants that are found in such 

 regions are thrifty enough and the only reason that sand bar- 

 rens are not more thickly populated seems to be the difficulty 

 experienced by similar plants in getting started. The same 

 is in a measure true of water plants which have nothing to 

 fear from an invasion of the plants on the shore. 



We may never know exactly how important the varying 

 soil characteristics are in determining the habitats of plants, 

 but that they are often the chief factors in the spread of cer- 

 tain species cannot be doubted. We are frequently at a loss 

 to account for the aggressiveness or the lack of this quality in 

 plants, unless we attribute it to the soil. There is probably 

 not a single species of plant that, in a locality exactly suited to 

 it, would not run out any other species. It is not mere aggres- 

 siveness in plants that, in a v/ild garden, determines which 

 species shall survive and which shall perish. Change but the 

 soil conditions and many of the dominant species would soon 

 disappear. In planting a border of wild things we set but a 

 single sprig of some things and soon have it in plenty, while 

 other species, growing luxuriantly enough in the locality 

 from which we brought them must constantly be attended if we 

 would have them live. Since aggressiveness in plants is thus 

 seen to be so largely a matter of soil and location, the intelli- 

 gent gardener will exercise more than the usual amount of 

 thought in the selection of a proper place for planting a new 



