1915] CURRENT LITERATURE 65 
communities. The first article characterizes the alpine zone as the area below 
perpetual snow and above the forest line, including for convenience the transi- 
tional area in which subalpine Krummholz and scattered trees alternate with 
alpine grassland. A number of the factors which together determine the posi- 
tion of timber line are discussed. The writer’s opinion that deficiency of rain- 
fall, or of precipitation in proper form, is an important factor preventing 
tree growth in the alpine zone may be questioned. In the table of precipitation 
for various points in Colorado given by Rossrns (Bor. GAZ. 49:260. 1910), 
Pike’s Peak has the highest mean annual rainfall listed, 28.65 inches; July 
and August, when alpine plants are most active, are the rainiest months. The 
influence of mountain masses is given by RYDBERG as tending to moderate con- 
ditions, so as to allow trees to extend to higher elevations. This effect may 
not be so general, for some botanists believe the presence of surrounding . 
mountain masses have the. opposite influence in some cases. Few observers 
would agree with RypBerc in classing Long’s Peak, in the Front Range, with 
Pike’s Peak and Sierra Blanca as isolated mountains. The question may be 
regarded as still open. 
In the second article the regions in which the alpine species have prob- 
ably originated (perhaps it would be better to sae the geographic sources 
from which they have probably been derived) are discussed, with lists for 
each region and lists of species common to two or more regions. The author 
is of the generally prevalent opinion that most of our alpine plants reached their 
present scattered stations during glacial times, when the circumpolar arctic- 
alpine flora was practically continuous over much lower latitudes and altitudes 
than at present. More than one-third of the species are restricted to North 
America. About 100 species from the subalpine zone extend higher than the 
forest line, and the purely alpine plants number about 250 species 
The third article is an account of the associations. ‘The cornmcinitis are 
called formations (in the specific sense in which the term association is generally 
used); they are based on habitat as determined by topography. They are: 
(1) rock-slide formation of rock-slides and rock-fields; (2) the generally dis- 
tributed mountain crest formation of areas thinly covered with gravelly oh 
(apparently this corresponds to the dry meadow of Cooper, Bor. Zo: 
324. 1908); (3) mountain seep formation; (4) alpine meadow; (5) alpine or 
(6) alpine lake or pond; (7) cliff ST, (8) snowdrift formation. It i 
perhaps a question whether some of the associations might not better have as 
characterized and named from the vegetation itself rather than from the 
bitat. The lists of species are full; those extending into the lower mountains 
are distinguished, and also those characteristic in, or confined to, the northern 
or southern parts of the Rocky Mountain region. Hardly any information is 
given to indicate which species are most frequent, abundant, or characteristic 
in particular associations. The alpine zone is really well known to very few 
tanists, and articles dealing with its vegetation are not numerous, thus 
giving the present writing so much the greater value—ARTHUR G. VESTAL. 
