Plate 25 



XSC S-4-a. Branch section of Ciiprcssiis arizonica, cut May 13, 1941. Xylem of 



1937-1941. Multiplicity and growth layer contacts — weak annuals and also 



weak intra-annuals ; "outer thin" gl with faint indefinite dw ; ddw. 



1937: see, masked partially by slight frost injury at start of 1938. 



1938: Incipient inner natural frost; effects of natural frost with dw cells; 

 faint dee ; see ; see with strong dw and ddw. 



1939 : see with strong outer dw over part of circuit and very weak dw over 

 a lens. Note contrast of outer margins over various parts of cir- 

 cuit. The lens definitely a second cycle of cambial activity. 



1940: msce ; s arc; 2 see (contacts of intra-annuals become less sharp out- 

 ward on branch). 



1 941 : inc. e gl, to May 13. Branch frozen May 9, 1941, 13.5 cm. outward 

 from this section. 



(Low magnifications on unstained sections without criteria of absolute dating 



would encounter difficulty in distinguishing all annual from all intra-annual 



contacts.) 



