424 BOTANICAL GAZETTE [MAY 
Tree growth.—Douc Lass* hopes to find in tree growth an indicator that 
may be used for estimating rainfall, but the preliminary steps of his investi- 
gation are similar to those of botanical observers. Studying Pinus ponderosa 
grown in the northern plateau of Arizona, a semi-arid region where the amount 
of precipitation is almost certain to be the limiting factor of annual growth, his 
conclusions agree with those of KrrKwoop in indicating the importance of the 
precipitation of the fall and winter months upon the amount of the increment 
of the succeeding growing season. Further, a most satisfactory explanation 
of double annual rings is found in the failure of fall and winter precipitation 
when the resulting spring drought is followed by the usual heavier rainfall 
of July and August. Sometimes when this drought is excessive, the later rains 
do not seem to be able to stimulate a late summer growth, and a very narrow 
single ring results. In a few instances Douciass thinks that, for some 
unknown reason, there has been the entire suppression of one annual ring. 
From measurements of annual rings, given in detail in a previous paper,%: 
a growth record is obtained for the past five centuries. When this is plotted 
as a curve and a comparison made between an available rainfall record for the 
region extending back to 1867 and the portion of the growth curve for the 
corresponding period, there is found an agreement of 80 per cent, but we are 
warned that such an agreement is likely to obtain only for a dry climate. An 
effort to discover a regular periodicity in the growth rate is rather unsuccessful, 
although there seems to be some agreement with the sun-spot cycle of 11.4 
years.—Geo. D. FuLrer. 
hydrarch succession.—MATrHEws* has reported on the study of the 
succession of plant associations occurring in the gradual filling up of a pond 
of some 16 acres in area situated in Perthshire, Scotland. Aquatic and marsh 
associations of the usual type are found, but with an unusual paucity of species. 
—Geo. D. FULLER. 
%° Doucrass, A. E., A method of estimating rainfall by the growth of trees. 
Bull. Amer. Geogr. Soc. 46:321-335. 1914. 
3t Weather cycles in the growth of big trees. Month. Weather Rev. 
37:225-237. 1909. 
3? Marruews, J. R., The White Moss Loch: a study in biotic succession. New 
Phytol. 13:134-148. figs. 2. 1914. 
