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THE AM EE WAN NATURALIST [Vol. XLIII 



temperature, others could not be made to do so until they 

 had been subjected to temperatures approaching the 

 freezing point. These latter were seeds of winter an- 

 nuals, and by this method a fundamental physiological 

 difference between them and the summer annuals was 

 established. Doubtless an indefinite amount of instruc- 

 tive and necessary work remains to be done in this direc- 

 tion, but the key to the situation was found in carrying 

 out the simple experiments described. Again, partly as 

 a relief from severer work, Dr. Cannon undertook, in the 

 midst of his investigations at the Desert Laboratory, to 

 map the distribution in the soil of the roots of some of 

 the plants growing in the vicinity. Hardly was the work 

 well in hand, and the root topography of less than half 

 a dozen species mapped, when it was found that the clue 

 to certain facts of distribution, blindly observed up to 

 that time, had been discovered. I have spoken of this 

 in more detail in another connection. 



Obviously it is indispensable that determination of 

 physiological data and of those belonging to the physical 

 environment should proceed step by step together; and 

 nowhere is this more strikingly true than in the investi- 

 gation of soil relations. To refer to one more case of 

 recent experience,— within the past year Dr. Livingston 

 has determined the percentage of soil moisture present 

 in soils obtained from each of the topographic areas of 

 the Desert Laboratory domain and the adjacent flood 

 plain of the Santa Cruz River. His studies were con- 

 ducted independently, though naturally not in ignorance 

 of ecological studies which were being carried out at the 

 same time on the same ground. It now appears that a 

 well-nigh perfect correspondence exists between the two 

 sets of facts obtained by independent workers, so perfect, 

 in truth, that a causal relation offers the only satisfac- 

 tory explanation. The accumulation of physical data, 

 however, has proceeded so far and so satisfactorily that 

 the successful conduct of this line of investigation may 

 be regarded as assured, but for the plant the relations 



