No. 512] PRESENT PROBLEMS IN PLANT ECOLOGY 485 



adjustment is such that they grow just as well or hetter 

 along an irrigating ditch carrying fresh water. Various 

 other plants in the immediate neighborhood have not In- 

 come adapted to the conditions prevailing in the salt 

 spots, nor do they appear capable of adjustment to them, 

 and accordingly are not found growing in such places. 



We need not multiply citations of these familiar eases. 

 Adaptation and adjustment have long been words to con- 

 jure with, out of the desert as well as in it, but we have 

 made so little real scientific progress in the definition and 

 determination of the things for which they stand, that 

 some of our foremost students of ecology seem ready to 

 abandon the effort, while others apologize when they use 

 the terms, as if they were myths and had better be left 

 alone. But nothing is gained, and much may be lost, by 

 this method of procedure. We are face to face with a 

 great body of phenomena of the most striking character, 

 in connection with which these words are fittingly em- 

 ployed. We can not ignore the existence of the facts, 

 and as scientific men we can not let them alone, while 

 they insistently rise at every turn in our pathway and 

 demand investigation. True it is that they bring m 

 their train whatever is fundamental in biological inquiry 

 —heredity, the direct influence of the environment, and 

 differences in the properties of protoplasm in different 

 plants. It is not customary, however, in laboratories 

 worthv of the name, to shun investigations that approach 

 to the deep mysteries of life. There is every reason why 

 students of ecological problems should seek, not slum, 

 this difficult but hopeful line of study. I say hopeful ad- 

 visedly, for within the past three years there have come 

 under* my observation various definite cases of adjust- 

 ment in plants, some of which have been accurately meas- 

 ured, correlated with external factors, and expressed 

 by curves Though essentially more difficult, there is no 

 reason, as far as now appears, why the different degrees 

 of adaptation of two species or varieties to a given ex- 

 ternal factor may not be similarly determined and 



