380 BOTANICAL GAZETTE [NOVEMBER 
find them in intermediate situations. Another explanation must 
be appealed to. It is probably found in the uplift at the close 
of the Cretaceous period, followed by the subsequent base- 
leveling operations. While the eastern United States, including 
that part of New Jersey along the Delaware River, was an almost 
featureless peneplain during the close of the Cretaceous, it is con- 
ceivable that the plants above mentioned had a more general 
distribution, and that when the uplift of the Appalachian system 
occurred and the formation of the Tertiary coastal plain was 
well under way, these plants, then widely distributed, were sub- 
jected to the influences of the processes of gradation. The 
wearing away of the soil from the mountains, the formation of 
valleys, and the oscillations of the coast line led to a process of 
extermination, and many plants succumbed in those regions to 
the geologic changes. The survivors of many widely distributed 
groups of plants are found, therefore, in those places that resisted 
the action of the destructive forces, such as the present summits 
of high mountains, or are in regions not subjected to the oscil- 
lations in level of the coastal plain. This supposition is sup- 
ported by the suggestion of Cowles, that in all probability 
these plants survive under such conditions because the summits 
of these mountains and the sandy coastal plain are in about the 
same stages of their life histories. It seems to the writer, that 
the similarity of the situations, which are in the same edaphic 
stage of their life histories, consists in this.35 ‘In the dry places, 
especially the insolated slopes of the high mountains, the humus 
is sour or ‘‘raw;”’ in fact, the dense tangle which roots often form 
in such situations is well known for its tendency to produce sour- 
ness by hindering aeration. Similar sour humus is found in the 
wet swampy forests. Sour humus makes it more difficult for the 
roots to absorb moisture, and consequently it becomes necessary 
for the plant to reduce transpiration. The lack of oxygen and 
pebieleion via shies of nitrogen in such soils still further induces a 
£ cok 
gi activity. It appears clear, therefore, that 
the abe sail importance of xerophilous conditions increases in 
33 This thought was suggested by a reading of a paper by ERNEST BRUNCKEN, 
Contributions to the ecology of the genus Viola. Bull. Wis. Nat. Hist. Soc. 2:27- 
