CHAPTER XV 



ORIGINATION OF SELF-GENERATING MATTER AND THE 

 INFLUENCE OF ARIDITY UPON ITS EVOLUTIONARY 



DEVELOPMENT 



D. T. MACDOUGAL 



Any attempt at an interpretation of a desert landscape, with its 

 diversity of forms, isolation of individuals, and scarcity of organic 

 matter in the soil, leads inevitably to a consideration of the theoret- 

 ical conditions which would be necessary in the origination of the 

 physical basis of life, its development into organisms known to us 

 in the living and fossil state, and also of the possibilities of the oc- 

 currence of a re-generation at the present time. 



From almost every excursion which the biologist has made into this 

 inviting field of speculation on which he has called to his aid various 

 extreme or unusual intensities of the factors to be taken into account, 

 he has been ruthlessly recalled by the geological historian with the 

 reminder that the general composition of the atmosphere, its pres- 

 sure, the temperatures, and other conditions prevalent on the earth's 

 surface were uniform and continuous with those now encountered 

 and not widely different, in their total departure, in any stage of 

 terrestrial development in which life might have originated. 



Now we are not able to discover that living or self-generating 

 matter is actually being formed anew on the earth's surface at the 

 present time, and in the absence of positive evidence we are com- 

 pelled to say that all life now in existence must have descended from 

 forms which had their ultimate origin in other times and under 

 other conditions than those now prevalent. 



A consideration of the phyletic aspects of fossil and living forms 

 of plants yields but little, which might serve as an indication of the 

 conditions under which the earlier forms developed. Even the earliest 

 remains include such advanced types as the ferns and cycads. The 

 amount of progress represented by the derivation of the gameto- 

 petalous seed-plants from these, in comparison with the preceding 



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