490 
GEOLOGY: E. BLACKWELDER 
live or developmental energy or of 'determiners' by repeated regen- 
eration but from changes in the non-regenerating part associated with 
age. In another place there is a discussion of the possibility that there 
may be an effect upon the rate of developmental processes in the or- 
ganism as a whole due to continued regeneration of a part. This is 
studied particularly in connection with the effect of regeneration upon 
rate of metamorphosis in Amphibia. 
Regeneration studies in general and those on successive regeneration 
in particular make it improbable that there is a definite number of 
cell regenerations between the fertilized egg and the end product, the 
differentiated cell. The possibility that certain cells may remain in an 
early cell generation can not be wholly excluded as an explanation of at 
least part of first regeneration phenomena. Under suitable stimula- 
tion such cells may be postulated to take up development where it has 
left off. The definite descriptions of de-differentiations of cells as well 
as other facts of regeneration argue against this conclusion. The view 
that there can be no such definite number of cell generations is strength- 
ened by the facts of successive regeneration. It does not seem probable 
that embryonic cells of an early cell generation can be held in reserve 
through repeated regenerations. 
The explanation of regeneration by the theory of duplicate sets of 
determiners meets difficulties in undiminished successive regenerations. 
The greater the number of repeated regenerations the greater the diffi- 
culties of explanation on this basis. Of course the difficulty does not 
hold for the hypothesis that every cell or nearly every cell contains a 
full set of determiners. 
The earlier appearance of the maximum rate in the second than in the 
first regeneration may be due to the more rapid progress of the cells in 
the early cell migration period alone or it may be due to the acceleration 
of the whole developmental cycle. 
The full data will be published in the University of Illinois Biological 
Monographs. 
THE GEOLOGIC ROLE OF PHOSPHORUS 
By Eliot Blackwelder 
DEPARTMENT OF GEOLOGY. UNIVERSITY OF WISCONSIN 
Received by the Academy. July 19. 1916 
Phosphorus appears in nature in many forms and in many situations. 
Its numerous transformations, however, follow an orderly sequence. 
In a broad way, the changes form a cycle but since the path of change 
