tgtt] CHAMBERLAIN—CYCAD TRUNK 87 
A plant of Ceratozamia mexicana, collected about 10 kilometers 
north of Jalapa, had a trunk 30 cm. high and 15 cm. in diameter. 
The pith, 5.7 cm. in diameter, was surrounded by a zone of zylem 
3 mm. wide, with phloem 2 mm. wide, beyond which was the cortex 
1.5 cm. wide, and surrounded by a heavy armor of leaf bases. 
A mature plant of Zamia floridana, with a stem 15 cm. in height 
and 6 cm. in diameter, had a pith 1.3 cm. in diameter, the zones of 
xylem and phloem each measuring 2 mm. in width, and the cortex 
about 2 cm. in width. The entire armor had disappeared, and a 
comparatively regular phellogen had become established in the 
cortex. _ 
A specimen of Dioon edule at Chavarrillo, with a trunk about 
60 cm. in height and 21 cm. in diameter, had a pith 8.7 cm. in 
diameter, the zones of xylem and phloem each measuring 5 mm. in 
width, the cortex 2 cm., and the leaf bases 3.6 cm. A taller speci- 
men, about 1 meter in height, but with the same diameter, had the 
following dimensions: diameter of pith, 6.9 cm.; width of xylem, 
1.5 cm.; width of phloem, 8 mm.; width of cortex, 3.2 cm.; width 
of leaf base region, about 1.5 cm. 
These measurements may be regarded as typical of most 
monoxylic trunks. The mount of wood in polyxylic trunks, though 
somewhat greater, is still so scanty that no exception to the con- 
ventional description has been necessary. 
Naturally, it was with considerable surprise that I noted, in the 
Tierra Blanca region, trunks of Dioon spinulosum with zones of wood 
4,6, and even ro cm. in width. A specimen 6 meters in height, and 
33 cm. in diameter at a distance of 30 cm. above the rock on which 
it was growing, had a zone of wood 10 cm. in width. The phloem 
was 1.4 cm. in width, the cortex 2.5 cm., and the armor near the 
base of the plant, where it had been greatly reduced, only 0.5 to 
1cm. The pith at a distance of 60 cm. below the apex was 8 cm. 
in diameter, and from this point to the base of the plant its diameter 
was uniform. What the extent of the wood in a specimen 15 or 
16 meters in height might be, remains to be determined. 
he numerous large medullary rays reaching from the pith to 
the cortex are a conspicuous feature of the transverse section (fig. 
3). Besides the large rays there are much more numerous small 
