NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. 243 



XSC i-5-a {1936-1940) 



2 sce+i msce + 8 sL + 3 psL + i dL + i s ^L + ddw— S years. (See 

 table 103, p. 165.) 



If we include 1930 to 1935, we must add 16 sce + 3 sL+i dL+i 

 ddw. 



Tree XSC i has a high degree of multiplicity, parts of which may 

 be exaggerated because of irrigation during 1936 and prior years. 

 Nonetheless, a rather high degree of multiphcity characterizes the 

 lower forest-border zone, accentuated downward or toward the drier 

 areas and diminished upward or toward the wetter areas. This fact 

 of multiple growth in an extreme lower forest-border situation, com- 

 bined with methods of absolute dating, make the Lubbock region 

 nearly ideal for learning what a tree can and will do in response to 

 highly variable growth factors. 



Two additional comments are suggested. First, nearly all of our 

 specimens are from branches. The evidence we do have, added to 

 the tracing of growth layers inward on the branches, indicates that 

 the trunks participate in multiplicity. If, in some cases, the record 

 in the trunks is subdued, in comparison with that in the branches, 

 then the branches are giving a more complete and more detailed 

 ecologic story. 



Second, without methods of absolute dating, the complexity of the 

 sections would make them useless for any information based on pre- 

 cise years. Wholly apart from this, however, the pattern formed by 

 the complex array of partial and entire growth layers testifies elo- 

 quently to the impact of highly variable growth factors. If fluctua- 

 tions of soil moisture are great and of paramount importance in a dry 

 climate, we receive an excellent idea of the rainfall regime which re- 

 charges the supply of soil moisture. 



XSC 2-i-a {1934-1940) 

 13 see -f- 13 sL + 2 ddw 4- inc— 6* years. (See table 104, p. 165.) 



Branch XSC 2-1 was cut ofif May 10, 1940, after having been frozen 

 artificially April 8, 1940. Sections a contain 26 sharply bordered 

 growth layers for 6 years — it is again obvious that a sharply bordered 

 growth layer is not necessarily annual. 



XSC 2-2 (1934-1940) 



a. 18 see -f I dee + 7 sL -j- i msL -}- i dL + arcs— 6* years. (See table 

 105, P- 166.) 



