NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. I33 



VARIATION OF SEQUENCES ON DIFFERENT SECTIONS OF THE 

 SAME BRANCH 



Variations among sequences along the length of a branch exist for 

 the same reasons that they do among different radii of one cross sec- 

 tion. However, they are neither so numerous nor so striking because 

 whole sections are compared rather than single radii. If various radii 



Fig. 41. — TTC 5-11-a. Increments for 1936-1940. Multiplicity and complex 

 lensing. 1936: 2 see; 1937: jL's ; rnsce; 2 see; sL; 1938: natural frost effects ; 

 long arc; msce; compound sL; 1939: frost spots; see; compound sL; 1940: 

 d 2L; see; compound sL. 



on one section were compared to various radii on the other sections, 

 the differences would be equally numerous and equally striking. This 

 is to be expected because partial growth layers are not only local 

 around the circuit but also local along the length of a branch. In 

 addition, a partial growth layer may be multiple in its existence longi- 

 tudinally. A lens, for instance, may be concurrent along the branch 

 as well as around the circuit of a cross section. 



Examples will be given for the double purpose of illustrating longi- 

 tudinal variations and the building of a well-rounded picture of 

 growth layers in all their manifold classes. Under the section on 

 longitudinal variations, in the chapter on classification, examples have 



