502 BOTANY. 
In concluding this imperfect sketch we would only add that for 
years this will be the standard work on the ornithology of North 
America, and that the volume or volumes on “t Water Birds” will 
be looked for with much interest by students and others interested 
in the birds of our country.— J. S. MERRILL. 
BOTANY. 
DISTRIBUTION or Atpine Prants.—M. De Candolle delivered 
at the late Botanical Congress at Florence a communication on 
the causes of the distribution of rare plants on the Alps. The 
author (M. De Candolle) explained that the preglacial Alpine 
flora was not able to exert a great influence on the existing 
flora, inasmuch as the great changes which took place during a 
glacial period had necessarily swept away this ancient vegetation. 
He could not agree with those who considered the Alps as 4 centre 
of diffusion of a special flora, but believed them rather to be the 
refuge ground for the plants, which, as the glaciers retired, had 
found conditions more favorable to their existence than in places 
lower down. In proof of this he observed that the richest pari of i 
the Alps for rare plants are those which were soonest deprived of 
glaciers, the ground having been thus cleared for the introduction 
of a more ancient flora, of which these rare plants arè remnants. 
The southern, the eastern, and the western slopes of the Alpat : 
successively cleared of the principal glaciers, and the Swiss Alps a 
received their flora first from the south, and then from the peas 
west. The author then asks, “ Why should the plants aoe we 
the glaciers retreat, and why should there be greater variety a 
this advancing vegetation?” In preglacial times there ice ee - 
moisture in the climate of Europe, and consequently the meee 
richer and more varied. After a time the climate became ae . 
and as the glaciers retired many plants were able to m 
themselves by advancing gradually over the ground as it rable 
unoccupied by glaciers, finding there conditions more ere a 
for their growth. Hence one can deduce the law that the p p 
and variety of Alpine floras depend on the antiquity % 
ntroduction. tain & 
_ Mr. Ball approved of M. De Candolle’s theory to 9 0° u 
tent, but he did not consider it sufficient to explain all the that : 
When, for instance, a rare species is to be found in we 
