NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. 1 67 



1939 are exterior, and the densewoods interior to the lenses are di- 

 vided, showing that, locally, the cambium and the maturation proc- 

 esses experience multiple rhythmic activity within single growing 

 seasons. Although the number of growth layers in 1940 appears 

 rather excessive in view of the cutting date, a relatively few cells rep- 

 resent each growth layer radially. All our observations and ex- 

 periments indicate the rapid formation of xylem early in the season. 

 Nevertheless, it would be quite worthwhile to repeat the experiments 

 and observations in order to verify the amount of xylem formed by a 

 date which appears to be rather early in the season. 



Table 107.— XSC 3-1 

 Sj cm. 68 cm. S3 cm. 



1936-1937 7 msce 4 msce 8 msce 



I msL 



2 sL 2 sL 



ddw ddw 



1938 I see I see i see 



I msec 



2 sL 2 psL I sL 



1939 I see I see i see 



I msL 2 msL i sL 



I psL 



I d arc 



1940 2 see 2 see 2 see 



2 sL I msL 



4 dL I dL 



ddw ddw 



inc L inc inc 



XSC 3-1 (table 107) was frozen artificially at 68 cm. on April 11, 

 1940, and was cut off May 26, 1940. Dating was based on natural 

 frosts. Even if a frost were sufficiently atypical to confuse dating, 

 multiplicity and abundant growth would be characteristic if 1935 is 

 kept barren of frost effects, as it must be. In 1938 at 85 cm., the sharp 

 lenses are compound ; in 1939 at 85 and 68 cm., one set of lenses is 

 compound and the other set overlapping. 



Freezing and cutting dates for XSC 3-2 (table 108) coincide with 

 those of XSC 3-1. The lenses of 1936 at 112 and 95 cm. are com- 

 pound; those of 1937 at 80 cm. are concurrent, some sharp, the rest 

 diffuse. In 1938 the lenses are compound. In 1939-1940 the mostly 

 sharp lens is concurrent. 



XSC 6-1 (table 109) was frozen artificially April 8, 1940, at 1 18 cm. 



