198 BOTANICAL GAZETTE [FEBRUARY 
(2) shade, increasing permanency; (3) wind, tending to decrease duration; 
(4) moisture, tending to lengthen duration; and (5) bog habitat, causing the 
same early fall as dry habitat. In general, factors which cause increase in 
transpiration are accompanied by decrease in leaf duration, while those factors 
tending toward decrease in photosynthetic activity are accompanied by 
increased duration. The author of the paper is to be commended upon its 
good organization.—Gero. D. FULLER. 
Physical factors in plant distribution—The recent advances along the line 
of devoting more attention to the factors controlling vegetation and the 
progress made in more correctly evaluating these factors have been discussed 
y SHREVE,% who has also pointed out the striking contrasts in the physical 
conditions of mountains in humid and arid regions. The contrasts in humidity 
are most marked, but are manifest also in temperature and light. Examples 
are seen in the Blue Mountains of Jamaica, with a daily temperature range of 
6-10°, compared with the Santa Catalina Mountains of Arizona, with a daily 
range of 40-65° and corresponding annual amplitudes. These and other 
differences enumerated result in plant associations where a stratified rain 
forest in the former region, with large trees, under trees, shrubs, large herbs, 
and small hygrophilous plants superimposed in luxuriant profusion, contrasts 
with the scanty shrubs, the open pine forests, and somewhat denser fir forests, 
all almost devoid of any ae whatever, which are distributed over the 
slopes of the latter.—Gro. D. FULLER. 
Anatomy of Betulaceae.—The intensive anatomical work among the 
osperms has forged an unusually effective weapon for attacking phy- 
logeny, and it is beginning to be used in the interpretation of angiosperms, 
with very interesting results. Hoar*’ has investigated the anatomy of the 
Betulaceae and has come to the conclusion that the group belongs “near the 
base of the dicotyledons,” and that Alnus most clearly illustrates the primitive 
conditions. In this genus the aggregate condition of rays is either normally 
developed or in a state of reduction, while in the more advanced genera (Car- 
pinus, Ostrya, and Betula) the aggregate condition persists only in conservative 
regions or is ‘‘recalled by injuries.”” The conclusion of course depends upon 
the position of the aggregate ray in the phylogenetic series of ray structures. 
In the same connection Casuarina was investigated, the result being to confirm 
its low position among the dicotyledons, and also its close anatomical relation- 
3 SHREVE, Forrest, The rast . physical factors in the study of plant dis- 
OE, Plant World 19:53-6 
——, The physical mee ae in rain forest and desert mountains. 
aes World 20:135-141. 1917. 
Hoar, Cart S., The anatomy and phylogenetic position of the Betulaceae. 
Amer. Jour. Bot. 3:415-435. pls. 16-19. 1916. 
