Plate 24 



Pig. I. XSC 6-i'b. Branch section of Cuprcssits aricoiiica, cut Alay 10, 1940. 

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

 plicity ; rhythms ; lensing. 

 1937: Bands of dw ; iL's ; see. 



1938: Circle of natural frost effects; bands of dw; see; sL. 

 1939: Spots by natural frost; bands of dw; |L; see; sL. 

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



Without the presence of absolute dating criteria, the ix)ssibility of error in 

 dating gls is obvious. 

 Fig. 2. XSC S-^^-b. Branch section of Cuprcssits arizonica, cut May 11, 1941. 

 Xylem of 1938-1941. Multiplicity; "outer thin" intra-annual ; "added-on" 

 lens of 1940; artificial frost injury; growth to a certain date. 

 1938: dee and see, resembling widely spaced ddw. 

 1939: Slight curtain effect; natural frost spots; parenchyma circle; see; sL 



which began as ddw and grades into a curtain in other direction ; 



"outer thin" see. 

 1940 : Curtain efifect ; parenchyma circle ; psce ; see whose dw separates by 



insertion of Iw, outer contact weakened ; "added-on" sL. 

 1941 : inc. e gl ; most recent cambial derviatives and initials disrupted by 



artificial frost of May 9. Wettest April and May on record. 



