l64 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I40 



interior lens made up entirely of compression wood whose outer cells 

 are narrow for half the extent of the lens. On the short radius, the 

 lightwood of the outer, sharp, complete, entire growth layer is reduced 

 to a width of one cell which is narrow itself when compared with the 

 lightwood cells at the start of 1936. These features combined with 

 weakness of the densewood make it difficult to resolve the growth 

 layers except under high power. Under low powers, especially, the 

 definition of a growth layer may depend more upon the characteristics 

 of the growth layer succeeding it than it does upon its own charac- 

 teristics. 



ipsd, at 107 cm. — The two growth layers designated mostly sharp, 

 complete, and entire are thin and lie at the start of the annual incre- 

 ment. At the outside of the chief growth layer there is a 200° sharp, 

 thick, heavily lignified lens. At 89 cm. — On the long radius the inner 

 sharp, complete, entire growth layer has a compound lens of two mem- 

 bers ; the next outer sharp, complete, entire growth layer likewise has 

 a compound lens ; and the third sharp, complete, entire growth layer 

 has a long interior lens. All together, the increment of 1936 at 89 

 cm. has five lenses arranged radially. Close examination shows that 

 the interior lens actually possesses densewood which is entire around 

 the circuit. The fifth lens lies on the long radius at the outside of the 

 increment. 



ip3/, at 107 cm. — Considerable detail will be given to illustrate the 

 complexity of an annual increment. The 1937 increment consists es- 

 sentially of two entire growth layers of highly variable relative thick- 

 nesses. The inner growth layer has a huge bulge on one radius 

 whereas the outer has one on a different radius. In the bulge of the 

 inner growth layer, there are two sharp exterior half-lenses which 

 face each other and whose densewoods are continuous as a diffuse 

 band. At the bulge of the outer entire growth layer, the great thick- 

 ness is made up of a sharp lens which contains within it a sharp half- 

 lens, divided densewood, and a sharp overlapping lens in addition to 

 various bands of densewood. The 1937 increment at 89 cm. possesses 

 complexity equal to that at 107 cm. Here the transgressive, or over- 

 lapping, lens is in the inner group of growth layers. 



At 92 cm. in XSC 1-5 (table 103) five of the lenses are compound, 

 that is, radially placed, and two are concurrent. Both 1938 and 1940 

 increments at 92 cm. appear to be represented by lenses. However, it 

 is highly probable that only the lightwoods are lenticular. Longi- 

 tudinal variations in the constitution of the annual increments are only 

 too apparent in XSC 1-5. 



