88 BOTANICAL GAZETTE [AUGUST 
ones. Both kinds of rays have a comparatively slight longitudinal 
extent. Each large medullary ray contains a leaf trace bundle, 
but the small rays are in no way connected with bundles. 
GROWTH RINGS.—Dioon spinulosum has well-developed growth 
rings, a feature which, so far as I know, has not been described for 
any cycad. These rings are conspicuous in the upper part of the 
trunk, and can be recognized even in the lower portions of old 
plants (figs. 3 and 19). That the rings are growth rings, and that 
Fic. 3.—Dioon spinulosum: transverse section of lower part of the piece shown in 
fig. 2; note the large and small medullary rays, the growth rings, and the large amount 
of phloem; X#. 
they have approximately the same structure as the annual rings of 
dicotyls, is obvious from a glance at a transverse section; but that 
they are annual rings is doubtful even in Dioon spinulosum; and 
in D. edule, where the rings are equally conspicuous, it is abso- 
lutely certain that they are not formed annually. 
A transverse section of the 6-meter plant of Dioon spinulosum, 
already mentioned, at the level of the third crown from the apex, 
showed four growth rings. This piece had borne one cone. A sec- 
tion of the same plant at the level of the eighth crown below the 
apex showed 13 growth rings. During the formation of the nine 
crowns the plant had produced at least 8 cones. 
