1915] CURRENT LITERATURE 343 
In a more extensive investigation, KAPTEYN? regards it important that 
the data of tree growth, to be reliable, should be from trees in rather extensive 
forests, well situated with respect to subsoil water, and where the conditions 
over considerable areas are uniform. His own data were derived from annual 
ring measurements of oaks taken from the forests along the rivers Main, 
Moselle, and Rhine, and include the increments for the past two centuries. 
During this period the fluctuations in growth rate showed parallel variations 
in the three forests, and these variations correlated with meteorological records 
lead him to the conclusions that: (1) the very considerable fluctuations in the 
yearly growth of the oaks in the forests under consideration must, in large 
part, be due to meterological influences; (2) temperature has had a very small 
influence; (3) the rainfall of the spring and summer is the factor of the most 
rather than by any more direct action of greater ae (5) for at least 
the last 70 years of the period there was but a single growth ring produced each 
year; (6) there appears to be a rather constant periodicity of 12.4 years in the 
t 
indicate the importance of more extensive data before very definite con- 
clusions can be reached.—Gro. D. FULLE 
First-generation maize hybrids.—CoLtins® has described a method of 
comparing the yield of first-generation hybrids between distinct varieties of 
maize with the yield of the parent varieties. The principal difficulties with 
methods heretofore in use are thought to have arisen from failure to appreciate 
(t) the importance of individual diversity in such hybrids as well as in the 
parent varieties, (2) the abnormal behavior of self-pollinated maize plants, 
and (3) the necessity of securing for the comparison hybrids and parents of 
identical ancestry. Briefly, the method suggested for obtaining the material 
for comparison is to select two plants, r and 2, from each of two varieties, 
A and B, and by hand-pollination to make the four combinations represented 
by ArX A2, A2X Br, BrXB2, and B2XAr, resulting in one cross-pollinat 
ear of each variety and two ears representing the hybrid between the varieties. 
The reviewer does not doubt that, if a considerable number of these sets of four 
ars were similarly obtained, the method would afford an accurate means of 
comparing the yields of maize varieties as they exist with the yields of first- 
generation crosses between these varieties, and that it should therefore be of 
belies crete 
* Kapteyn, J. a ra growth and meteorological factors. Rec. Trav. Bot. 
Néerland. 11: 70-93. 
* Cottins, G. N. a more accurate method of comparing first-generation maize 
hybrids with their amends, Jour. Agric. Research 3:85-91. 1914. 
