tort} CHAMBERLAIN—CYCAD TRUNK IoI 
even more striking, the medullary rays being just the same, and the 
bast fibers having about the same arrangement as the long tracheids 
of the xylem. This structure makes the phloem nearly as rigid 
as the wood. 
Fic. 19 
Fics. 19, 20.—Dioon spinulosum: fig. 19, photograph showing growth rings, 
x; fig. 20, a single growth ring (g); 125. 
Rays.—In a transverse section the large medullary rays are as 
conspicuous as those of Quercus, and the small rays, while not 
nearly so conspicuous, are readily visible to the naked eye (fig. 3). 
The small rays vary greatly in longitudinal extent, some showing 
only a single cell in tangential section, while others may show 
more than 50, and may reach a width.of 3 or 4 cells. The great 
