74 BOTANICAL GAZETTE [JANUARY 
Anatomy of the node.—An example of what sort of contribution may be 
made by real “‘comparative’”’ anatomy to taxonomy is seen in SINNOTT’s work 
on the node of Dicotyledons.33 It has frequently been proposed to use the 
structure of the petiole in establishing relationships, but this region is subject 
to too great ecological variation to yield results of general significance. In 
the basal region of the leaf, however, a simpler and more constant condi- 
tion is found, and the number of leaf traces is characteristic of great 
groups. With respect to the Angiosperms it is concluded that the primitive 
number of traces is three, and that evolution has taken place in two directions: 
(1) by increase, as in Umbelliflorae; and (2) by reduction to one trace, which 
rence of transitional forms and by the fact that seedlings frequently show a 
simpler condition of the leaf trace than does the adult. Such a study supports 
the validity of a number of ENGLER’s orders, while it casts doubt on certain 
orthodox views, such as the near relationships of Compositae and i 
ceae.—M. A. CHRYSLER. 
Studies of desert vegetation —SHREVE* has studied the influence of low 
temperatures on the distribution of the giant cactus, Cereus giganteus, and 
he concludes that the limiting factor in regard to distribution northward is the 
number of consecutive hours of freezing. Plants exposed experimentally to 
freezing for six to fifteen hours were not seriously injured, whereas an exposure 
of more than thirty hours to freezing temperatures resulted in death. It is 
concluded that the giant cactus cannot exist where an entire day occurs without 
thawing temperatures. ohare the distribution of many other plants of 
the warmer deserts are thus lim 
HREVE5s has studied also oh eatatidancat behavior of the palo verde, 
Parkinsonia microphylla. Out of 542 seedlings of the year 1910, observed in 
their natural habitats, only 62 remained alive at the end of sixteen months. 
Further observations showed that a number of seedlings die in the second and 
third years, whereas most plants attaining the age of three years are fairly 
established and live for along time. Physical conditions, rather than competi- 
tion with other plants, are the chief factor in producing these results, and the 
most important physical condition is the absorption-transpiration balance.— 
H. C. Cowes 
33SrnnoTT, E. W., Investigations on the phylogeny of the Angiosperms. I. 
The anatomy of the node as an aid in the classification of Angiosperms. Amer. Jour. 
Bot. 1:303-322. pls. 30-34. 1914. 
S Forrest, The influence of low temperatures on the distribution of the 
giant cactus. "Plant World 14:136-146. figs. 3. 1911 
, Establishment behavior of the palo ane Plant World 14:289-296- 
Igil. 
