1gtt] | CHAMBERLAIN—CYCAD TRUNK 95 
The vascular connections are rather complex. Naturally, each 
cone dome must, at some point, surround the apex of the preceding 
cone dome. The general course of the bundles may be seen in 
fig. 7, which shows three cone domes, the lowest shown in transverse 
section, the next terminating in the base of an old peduncle, and the 
upper one passing into a young cone, while at the right of the 
young cone is the new growing point. It is evident from this 
figure and the preceding one that the traces of foliage leaves first 
touch the stele at its periphery, while the bundles of the cone domes 
are on the inside. 
As long as the new dome is separated from the rest of the vascu- 
lar tissue by a zone of pith, a transverse section looks like a section 
of a polyxylic stem, except that the smaller zone of vascular tissue 
is inside (fig. 8); but a little farther down, a transverse section 
presents a confused array of bundles (figs. 9 and 10). After the 
bundles of the cone dome and those of the previously formed wood 
have become arranged into a fairly regular zone, a cambium is 
established, and the formation of secondary xylem and phloem 
egins. In uniting with the previously formed wood, the course 
of the various strands of a bundle is not uniform, some going up, 
some down, and others entering more or less transversely (fig. 11). 
It follows necessarily that every cycad which bears terminal 
cones must have cone domes in the pith. This would include all 
the living cycads, with the single exception of the ovulate plant of 
Cycas, in which the sporophylls are borne in a loose crown like the 
foliage leaves, and the growing point is not transformed into a cone, 
but remains meristematic. It is possible that in specimens of 
Encephalartos, which produce several cones in a circle, the meristem 
remains as in Cycas. In such a case, no cone dome would be 
formed; but if at any time such a plant should produce only one 
cone, or two or more cones in a cluster, a dome would be formed. 
In Macrozamia Fraseri, WoRSDELL (6) found numerous bundles 
in the pith, but claimed that they had no relation to cones. This 
species usually bears only a single cone, and consequently must 
have cone domes in the pith. It is possible that WorsDELL’s 
plant, being a greenhouse specimen, may never have produced a 
cone, but Dioon edule, which elongates very slowly, may show as 
