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git] COWLES—VEGETATIVE CYCLES 163 
In this instance it is likely that some of the northern coniferous 
stages correspond to some of the southern oak stages; thus we may 
speak of alternative or substitute stages, when different plant forma- _ 
tions occupy equivalent places in a successional series. 
In a desert climate an upland may exhibit almost no succession, 
since the original xerophytic formation may remain with but little 
change; in comparison with a successional series in a mesophytic 
climate, one may speak here of the elimination of certain stages. - 
In marked contrast to the lack of succession or to the slow succes- 
sion on a desert upland is the rapid succession on uplands in humid 
climates; indeed, it is possible here for mesophytes to exist side by 
side with xerophytes in the pioneer stages—in such a case one may 
speak of telescoped successions. Even in a climate like that of the 
eastern United States, telescoping may take place, as in the suc- 
cessions of rich fallow land and in those which follow the cutting of 
&mesophytic forest. With this brief survey of recent progress in 
the field of physiographic ecology, we may pass to a similarly brief 
consideration of the historical development of vegetative dynamics, 
and then to a consideration of the main theme of the address. 
2. The development of dynamic plant geography 
The systematic exploitation of developmental or dynamic plant 
Seography presupposes the establishment of the principles of 
dynamic geology and of organic evolution; hence it could not have 
antedated Lyext, who brought general recognition of the former, 
or Darwin, who brought general recognition of the latter. Results — 
frequently lag far behind their causes, and it is only now, a full 
half-century after the publication of Darwin’s Origin of species, 
and three-quarters of a century after the appearance of LYELL’s 
Principles, that the dynamic method is coming to be regarded as 
the most fundamental thing in plant geography. As in other 
branches of science, there have been prophets far in advance of 
their time, though it is only within the last decade that the 
Prophetic insight of these pioneers has had recognition. LYELL 
tecords the Struggle of the developmental idea in geology, as 
°Pposed to the ruling theories of special creation or catastrophism, 
noting especially the keen philosophy of certain ancient Greeks 
