Plate 4. 



Fig. I. TTAp 2-i-a. Branch section of Mains sylvcstris, cut April 21, 1940. 

 Xylem 1938- 1940. Natural multiplicity and multiplicity caused by irrigation; 

 intra-annual dw more definite than annual. 

 1938 : 2 see, inner thick, outer thin. 

 1939: 2 see, inner thick, outer tliin and induced by 4-inch irrigation of July 



25, 1939- 



1940: Growth to April 21. 

 Fig. 2. TTC i-io-a. Branch section of Ciiprcssus arizonica, cut April 21, 1940. 



Sequence probably of 1938-1940. Irregular outer margins ; facing half lenses ; 



growth to April 21. 



1938 : Circle of parenchyma cells ; ddw ; ce gl with irregular outer margin. 



1939: Possible frost spot; arc of parenchyma cells; waves of highly lignified 

 cells ; 2 facing iL's, sharp at cusps, diffuse away from cusps ; fad- 

 ing dw, nonexistent dw or invisible margin; ^L's disappear within 16 

 cm. outward on branch ; ce gl with irregular margin. 



1940: Growth to April 21 ; 8 to 16 cells, immature on short radius, largely 

 lignified on long. 



