230 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I40 



is apparently no more characteristic of one part of a branch than of 

 another. 



Second, attention is directed to the complexity in the display of 

 growth layers — the mixture of entire and partial growth layers ; of 

 sharp, mostly sharp, partly sharp, and diffuse ; and the merging of one 

 type into another. If, occasionally, one encounters a situation such as 

 1938 in TTC 5-9-a (i sce+ 1 sL), he would have little or no reason to 

 suspect that the sharp lens does not represent an annual increment un- 

 less the growth layers are dated absolutely. The matter would be 

 viewed differently, no doubt, in regard to 1937 of the same branch (i 

 sce+ 1 msce). Suppose one were to study half the circuit and find two 

 fully developed, sharply bordered growth layers; he would have no 

 choice but to call them annual. Suppose now that the remainder of the 

 circuit should later become available and thus reveal on the margin of 

 of one of the growth layers a breakdown to diffuseness. Would that 

 indicate the growth layer to be intra-annual, or would it indicate that 

 the margin of an annual can be diffuse? The further discovery of sit- 

 uations such as 1937, TTC 5-10-a (isce+i msce+i sL), and 1939 (i 

 sce+i sL-fi psL), for instance, would convince the student that 

 many growth layers are not to be assumed to be annual unless ac- 

 curately dated. 



All this series of complex growth layers is visible on stained sections 

 under the microscope. On unstained sections, under a hand lens, the 

 weak, highly diffuse growth layers no doubt become invisible, and the 

 strong but diffuse-margined intra-annuals identify themselves. But 

 what is to be done about sharp, complete, entire growth layers, and 

 about sharp lenses and other partial growth layers? One of two 

 courses is open: first, the application of methods of absolute dating 

 which are restricted in scope or, second, an intensive investigation of 

 tree growth over a number of years in a given locality and of the 

 growth factors which promote that growth in order to make an intelli- 

 gent estimate of the number of intra-annuals per century. 



The complete story of a tree's response to its environment is re- 

 corded in the entire body of the tree and in all the growth layers 

 wherever they may be, whatever their extent, and whatever their 

 definition. 



Branch TTC 12-9 (table 18, p. 105) was cut off February 29, 1940. 

 Its summary for sections a (inner) reads: 



13 see -f- 6 psce + 3 dee + 3 sL + i d arc — 8 years. 



Some radii show many more sharply bordered growth layers than 

 there are annual increments. 



