go BOTANICAL GAZETTE [AUGUST 
hor the number of crowns less than 50, so that whatever the factor 
may be which produces the ring, it must appear at widely separated 
intervals. The trunk is obscurely ribbed, but the ribs do not cor- 
respond to the number of crowns, many crowns being represented 
in each rib. It is possible that these ribs are due to the resting 
periods during which neither crowns nor cones are produced. 
The number of rings may correspond to the number of these 
resting periods. It is possible that such resting periods may 
result in the formation of new zones of wood in polyxylic stems, like 
Cycas revoluta, and only in the formation of rings in Dioon edule. In 
either case, it would require time and some vandalism to secure 
evidence. 
ConE DOMES.—Vascular bundles in the pith have doubtless been 
seen by everyone who has cut a section of any mature cycad stem, 
but Merrentus (3), studying Dioon edule, was the first to interpret 
these bundles as the vascular system of the cones. Later, SOLMS- 
LausBacH (4) made a more thorough study of the pith bundles in 
Ceratozamia, and showed conclusively that the cycad trunk is a 
sympodium. Still later, the mode of development of the sympo- 
dium was described by Miss F. Grace SmitH (8), who studied the 
origin of young cones and stem apices in Zamia floridana. 
We have studied the pith bundles in Dioon spinulosum, D. edule, 
and Zamia floridana. In longitudinal sections of the stem, the 
bundles are in the form of a convex diaphragm, but since they 
really form a dome with the peduncle of the cone at its apex, we 
shall call the system of bundles a cone dome. 
The longitudinal section shown in fig. 4 contains five cone domes, 
the second of which, counting from the top, is cut through the axis 
of the peduncle, and the third and fifth show clearly the position 
of the peduncle, and the other two indicate its approximate location 
by a thickening of the bundles. In Zamia floridana the appearance 
is similar, but in Dioon edule, on account of the very slow growth, a 
single transverse section may show parts of as many as three cone 
domes. 
In transverse section the cone dome appears as a circle of vas- 
cular bundles more or less eccentric if cut near the peduncle, but 
concentric near the stele (fig. 5). 
