Plate 23 



Fig. I. XSC -="--'-(7. Branch section of Ciiprcssiis ari::oii{ca, cut May 26, 1940. 

 Portion of 1936 annual increment. Dw so distributed as to give appearance 

 of reversed sequence, lightest wood in the center. 

 Sequence as follows : 



(i) 2 cells of dw, with sharp contact that is masked by 



(2) dw, so close radially to dw of (i) as to give (i) a diffuse appear- 



ance; dw of (2) grades outward to 



(3) Iw. 



(4) dw with sharp outer contact. 



Lw grading both inward and outward into dw appears to give a reversed 

 sequence. Features change tangentially ; growing conditions induced dif- 

 ferent responses on different radii. 

 Fig. 2. XSC 6-i-a. Branch section of Ciiprcssiis aricoiiica. cut May 10, 1940. 

 Xylem of 1937-1940. Dating by natural and artificial frost effects; multi- 

 plicity ; ddw ; initial and well-developed departures from unity of annual in- 

 crement. 



1937: 2 sharp gls, outer with ddw. 

 1938: Circle of natural frost effects; see with ddw, the inner band of ddw 



separating more widely and becoming diffuse. 

 1939 : 2 see. 

 1940: Effects of artificial frost of April 8; inc. 



