Plate 3 



Fig. I. SA i~a. Stem section of shrubalthea, Hibiscus syriaciis, cut October 28, 

 1939. Xylem of I933( ?)-i939. Ring-porous angiosperni grown on a lawn 

 and watered periodically. Natural frost injuries in 1936 and 1938 ; partial gls ; 

 dw intermittent radially ; "invisible" dw. 



1933 (probably) : arc with invisible extension both directions tangentially ; 



see. 



1934 (probably) : Compound lens with intermittent dw and nearly "invisi- 



ble" dw : see. 



1935 (probably) : Thick lens with intermittent and invisible dw ; see. 

 1936: Frost injury; thin sL; see. 



1937: see. 



1938 : Frost effects ; see with intermittent dw. 

 1939: Thin see. 



Densewoods, whether intra-annual or annual, are intermittent tangentially. 

 Fig. 2. TRP i-i-a. Branch section of Piiiits aristata. cut June 2S, 1942. Typical 

 growth layers in a bristlecone pine ; thick and thin densewoods. Multiplicity 

 suggested by ilw one cell thick in 3d gl, and by presence of 13 diameter 

 flushes for 12 tip flushes (probable multiplicity in north-central New Mexico 

 at 9,000 ft. on a dry, steep, rocky slope). Elsewhere on section, 1942 growth 

 represented by lenses of immature cells ; in this case, therefore, diameter 

 growth preceded tip growth, of which there had been none up to June 28. 



