so THE SCIENTIFIC MONTHLY
the Santa Cruz. Booted in the aame aoil^ one may find species whose juice shows high and others whose cell sap shows low concentrations. Thus diversity or differentiation in the living organisms is not stnic- tnral merely. After a few weeks in the field, the observer will realize, more fully than he has ever before, that the distinctions between species are not solely of the kind that can be drawn or photographed or ascer- tained by inspection of that sacred and indispensable mummy, the type specimen. The species of plants are not merely externally dissimilar, but inherently very diverse; they are not merely morphologically differ- entiated but physiologically very distinct; they are to be distinguished not merely by their external form, but by their methods of reaction to the various factors of their environment.
In the greatest variety of ways these morphological and physiological differences are exhibited. Many of these have been briefly indicated in foregoing paragraphs. To enumerate in greater detail, the diverse modifications of the structural elements of which the flowering plant is typically built up or the variety of response to environmental factors would cany us too far into technical descriptions.
It is this great complexity of environment and this diversity of or- ganisms which render the southwestern desert one of the most fascinat- ing and profitable of all regions to the biologist, whether by specialization taxonomist, morphologist, physiologist or evolutionist
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