PROBLEMS OF TllE DESERT. 29 



Some general anatomical arrangements peculiar to the 

 vegetation of deserts are found to be widely prevalent 

 regardless of the phylogeny of the forms bearing 

 them, while the conditions enumerated are so sharp- 

 ly defined, and their variations so well marked, that 

 the relation of the plant in the desert to its en- 

 vironment take on the definiteness of an equation, offer- 

 ing a solution of some of the main problems of biological 

 science, most of the factors set forth being as capable of esti- 

 mation, and their action of measurement as the components 

 of an experiment in the laboratory. 



From the great group of inquiries solvable by such equa- 

 tions those pertaining to the origination of the structures, 

 qualities and capacities of organisms and the mechanism of 

 of the distributional movements by which the resultant forms 

 have reached their present positions may be selected for il- 

 lustration. 



The enclosed basins of Nevada, Utah, Central Asia and 

 Australia are examples of deserts in which much of the flora 

 must have come into existence in its present aspect within 

 comparatively recent periods. Furthermore the geological 

 record in some of these regions may be taken to have been 

 read with such fair completeness that the length of the 

 periods and the amplitude of the oscillations may be taken 

 as at least tentatively established and some general ideas upon 

 the relations between climatologlcal variation and the evolu- 

 tionary changes in organisms may be formulated. 



If an entire cycle had passed under the eye of a trained 

 observer, the opportunities for analysis would have doubtless 

 yielded the exact information by which some of our problems 

 might hav^e been solved. These lengthened investigations 

 being beyond us, our next recourse is to a duplication of the 

 conditions within time-limits during which continuous inves- 

 tigation may be carried on. Such duplication is offered by 

 the re-formation and un-making of the lakes in the desert 

 basins of the Colorado delta, with of course an enormous con- 



