ORIGINATION OF SELF-GENERATING MATTER 293 



make possible their maintenance as independent inhabitants of the 

 dry land. 



It is true, of course, that desert conditions are not favorable for 

 fossilization, yet many opportunities for such action undoubtedly 

 occur in the carrying and burying action of the torrential floods of 

 desert streamways, while wind-blown deposits might preserve the 

 more indurated forms. Many of these and the skeletons of the 

 Cactaceae would seem well adapted for preservation in this manner, 

 although no remains have yet been uncovered. The view that such 

 forms are of recent origin, within the present period of advancing 

 desiccation, would predicate a very great phylogenetic activity unpre- 

 cedented perhaps, but by no means impossible. 



The actual relationship between plants and their environment 

 is by no means a settled question and since this and related problems 

 are to be discussed in detail at the Darwin memorial session of this 

 meeting, this subject will not be considered here farther than to say 

 that it is unsafe to asssume that any organism has undergone adap- 

 tation and fitting specialization in direct somatogenic response to 

 any set of environic factors, and that admissible evidence on such 

 matters is extremely difficult to obtain.' 



The operations of factors lessening the supply of w^ater to any 

 region would of course result in greater aridity in some places than 

 in others and the movements of xerophytic forms established in 

 these to other contiguous areas dried out later would be a matter 

 in which the direction of the winds, streamways, movements of 

 animals, and position of mountain barriers would play a determin- 

 ing part. 



The recession of large expanses of water included in a desiccating 

 region, such as has occurred in the great basins in Utah and Nevada, 

 and in the bolsons t6 the southward and eastward in New Mexico, 

 Chihuahua, and Arizona would present special conditions. The rate 

 at which the waters of such inland seas might recede, however, would 

 be such that the advance of vegetation to cover the immersed areas 

 would be quite as rapid as that necessary to follow a receding ice- 

 sheet or a change of climate due to any cause. Thus our observa- 

 tions on the Salton Lake show that beaches a mile in width are bared 



I Fifty Years of Darwinism. New York: H. Holt & Co., 1909. 



