No. I'EEsEXT PROBLEMS IX I 'LA XT ECOLOGY 479 



spondingly more difficult. It seems likely that in tin* 

 study of ecological relations from the side of the plant 

 we shall employ more and more the methods and con- 

 ceptions of physics and mathematics, but the fact is too 

 patent to call for argument that neither now nor here- 

 after can these methods and conceptions he employed 

 exclusively. In fact there has never been greater need 

 than at the present time for exact observation coupled 

 with correct judgment, and these can never be replaced 

 or superseded so long as this department of botanical 

 investigation continues to he cultivated. This will re- 

 ceive additional emphasis in the following division of the 

 present paper. 



The relations of desert plants to each other present a 

 chapter, the importance of which has been unduly min- 

 imized until the general impression, even among botan- 

 ists, seems to be that desert plants are to be studied only 

 in relation to their physical environment; they are 

 thought to grow so far apart, in "open" associations, 

 that they are quite uninfluenced by each other's pres- 

 ence. Like other erroneous or incomplete conceptions, 

 this may be true in part, especially where the most ex- 

 treme desert conditions prevail, as for example in parts 

 of the Colorado or Mojave Deserts, but in the great semi- 

 arid region of the southwest, taken as a whole, it is most 

 misleading. The Desert Laboratory of the Carnegie 

 Institution was located where it stands on account of 

 the great natural advantages which the region and local- 

 ity offer for the study of desert plants in place, yet T 

 venture the assertion that over at least nine tenths of the 

 area of the laboratory domain the establishment of a 

 plant in the place which it occupies is conditioned quite 

 as certainly by the influence of other plants as by that 

 of the physical environment. It hardly needs more than 

 simple observation to convince one that severe competi- 

 tion is the rule, though naturally its severity is height- 

 ened and the result hastened by the prevailing adverse 

 physical conditions. 



