338 ‘BOTANICAL GAZETTE [APRIL 
the smooth pahoehoe was much more richly covered with vegetation, which 
occurred, however, only in cracks n a 1907 flow plants were found just 
beginning to be established. The author concludes that on both types of lava, 
the first pioneers are lower cryptogams; on the pahkochoe these are soon suc- 
ceeded by ferns and seeds plants, but on the aa there is a long-enduring lichen 
stage. Ultimately the natural forest of the region returns, except in places 
where man’s influence causes the successful invasion of a naturalized flora. 
koa (Acacia koa) is the dominating tree of the ultimate or climax forest.— 
H. C. Cow es. 
Rainfall and soil moisture.—In studying the conditions which govern the 
plant activities of the semi-arid region about the Desert Laboratory, Tucson, 
Arizona, SHREVE’ has made weekly determinations of the soil moisture at 
depths of 3, 15, and 30 cm. throughout the year, and compared the resulting 
data with the record of the rainfall for the same period, in order to see exactly 
how the former is affected by the latter. It is evident that precipitation of 
less than 0.15 inch has no effect upon the soil moisture, and that therefore 
there are periods of 140 days in the region under consideration without rain ' 
of sufficient amount to increase the moisture in the soil. This serves to indi- 
cate that in desert regions by no means all of the small rainfall is significant 2 
vegetation as a source of water supply. The evaporation has been determined 
and plotted along with its ratio to the soil moisture, the march of soil moisture 
throughout the year, and the distribution of rainfall, making an instructive and 
detailed chart of those moisture factors which affect vegetation. Among other 
things it proves the range of moisture conditions at the Desert Laboratory to 
be one of great extremes.—G. D. FULLER 
Drought resistance in Hopi maize.—For centuries the Indians of New 
_ Mexico and Arizona have grown a race of maize in soil that is much too dry 
for the ordinary races of the species. A large factor in the success of this race, 
known as Hopi maize (from the Hopi Indians), is the extraordinary capacity 
for elongation possessed by the mesocotyl.+ The Indians are accustom 
plant their maize at a depth of 15-45 cm.; this depth is for most varieties to 
can be induced in Hopi maize. Another advantage in the mesocot, 
maize is its ability to produce roots, a rare phenomenon in grass — ‘ 
A third feature of great importance is the great elongation of the primary 100 
. . bs 
%s SuREVE, F., Rainfall as a determinant of soil moisture. Plant World 17°90 ? 
Sigs. 3. 1914. 
4 Couns, G. N., A drought-resisting adaptation in seedlings of Hop! 
Jour. Agric. Research 1: 293-302. figs. 2. pls. 29-32. 1914. 
maize. 
