NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. 223 



The lower part of table 159 sets forth the branch relations for those 

 species from which a large number of branches was taken. No species 

 has significant divergence from the average of all branches except 

 TTP. Here the highest ratio occurs not in 1940, but in 1937, which in 

 all other branches had a comparatively low ratio. If TTP were sub- 

 tracted from the general average of all branches, the ratio of the latter 

 would drop much lower. There is outright disagreement between 

 TTP and all other branches in four years. The lowest ratios in TTP 

 occur in 1938 and 1945. If values of TTP be eliminated from the 

 averages of all branches, the former high and medium values will be 

 enhanced and the low values decreased. 



Insofar as the extent of the materials permits, table 159 shows 

 clearly that there is a marked difference among the years of record in 

 the incidence of multiplicity in branches. Further, certain years have 

 a high incidence of multiplicity whereas others have low incidence. 



The fourth and last question, asked at the start of the present sec- 

 tion, "What is the influence of the environment ?" has been answered 

 to some extent in passing. In the extreme lower forest border, there 

 prevails a persistent tendency toward multiplicity of growth layers in 

 the branches, not only with respect to intra-annuals that are sharp, 

 complete, entire, but also with respect to numerous partial growth 

 layers such as lenses, half-lenses, and arcs. This generalized influence 

 of the environment is undoubtedly of primary importance. The influ- 

 ence of different species, variation of local site factors from tree to 

 tree, and possibly the individual growth habits of a tree constitute the 

 factors of secondary influence. Nonetheless, they are of great im- 

 portance to a study of growth layers, not only in connection with details 

 of classification and occurrence but also in connection with the gen- 

 eral relationship between growth layers and climate. 



RELATIONS AMONG TREES OF THE SAME SPECIES 



Table 157 (p. 219) gave the flush agreement for the various trees of 

 the several species and was discussed on pages 215-220. On the whole, 

 the relations among trees of the same species seem to be more intimate 

 than among individual trees of different species, although this does 

 not mean a lack of striking variation within a species. 



From the above-mentioned table, it can be calculated that the aver- 

 age departure of the flush agreements within the trees of species TTC, 

 from the species average (table 158), is 18.2 percent, whereas for 

 TTP it is 15. These figures compare with the species averages of 58 

 and 25 percent, respectively. Hence, species TTC and TTP have 



