132 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, I40 



overlap, there are six sharply bounded growth layers for four years 

 on the entire section, no matter which radius is selected. But they are 

 not all the same growth layers. 



Fig. 40. — XSC 2-2-c. Increments for 1936- 1939, and portion of 1940. Part 

 of a section with simple multiplicity. 1936: Spots of natural frost; see; sL; 

 1937: see; compound sL; 1938: see; 1939: see; 1940: inc. 



Text figure 41, TTC 5-1 i-a, furnishes an apt summary of radial 

 variation. To be sure, the section seems to be exaggerated because of 

 decided eccentricity. Nevertheless, the numerous intra-annuals, which 

 are but partially responsible for the eccentricity, record the number 

 of times the cambium was stimulated into activity and also the num- 

 ber of times it became inactive. Another point in summary, this sec- 

 tion along with many others proves that annual increments can be 

 made up of multiple growth layers whose outer faces are sharply 

 defined. 



It is clear, therefore, that a single radius or an increment core from 

 one tree grown under certain environmental conditions would give a 

 rather inadequate record of the total growth of that tree ; even several 

 cores taken at one level or a substantial portion of a section would not 

 necessarily represent the remainder of the trunk. 



