tgi1] CHAMBERLAIN—CYCAD TRUNK 85 
crown. In fig. 1 the latest crown is tied to protect the bud, and 
the leaves of the crown below have been cut off. With this explana- 
tion, it will be seen that the upper portion has borne 8 crowns. 
The lower portion has borne 21 crowns, of which 6 or 7 toward the 
top are easily counted, while the rest are increasingly indistinct. 
How many crowns were borne by the intervening piece, about 4 
meters in length, and also by the stump, is not known, but roo 
crowns would be a very low estimate, and the plaht would be more 
than 100 years old even if a new crown were produced every 
year. 
Armor.—In some forms, like Dioon edule and Encephalartos 
Altensteinii, the armor of leaf bases is so persistent that each leaf 
base is distinguishable even in the lower portion of the trunk, while 
in Dioon spinulosum and others the leaf bases become indistinguish- 
able in the lower portion of old trunks. 
In Dioon edule, below the two green crowns constituting the 
foliage display and appearing as a single crown, is a crown repre- 
sented by decaying midribs from which most of the leaflets have 
fallen, and below this will be found one or more crowns represented 
by irregular jagged stumps, several centimeters in length, and it is 
only below these that one finds the smoothly cut off bases. The 
reason is easily determined. As in annually deciduous dicotyls, 
an abscission layer of phellogen is developed, but at so late a period 
that only a decayed stump of midrib remains to be cut off. After 
the stump has fallen, a new phellogen appears a little deeper than 
the first, and then another, so that successive phellogens keep scal- 
ing off the outer surface, even in forms with such persistent leaf 
bases as Dioon edule. At Chavarrillo, where this species is most 
abundant, the trunk is often damaged by fire. In such cases, where 
the entire armor may be destroyed, an extensive phellogen appears 
in the cortex, the meristematic layer sometimes reaching a width 
of several millimeters, and in this way a smooth protective covering 
is built up. 
In Dioon spinulosum the phellogens are more vigorous, and suc- 
cessive layers are scaled off until the leaf bases in the lower portion 
of old trunks become indistinguishable, and even the ribs due to the 
alternation of scale and foliage leaves become obscure. We have 
