82 BOTANICAL GAZETTE [AUGUST 
The excellent work of METTENTUs (3), published in 1861, deals 
with Cycas revoluta, Encephalartos horridus, Dioon edule, and 
Zamia muricata. The course and structure of leaf traces are de- 
scribed in detail, and spiral vessels are noted for the first time, 
these having escaped the observation of previous investigators, 
probably because in mature stems they are lacking next the pith, 
where one might expect to find them. He saw bundles in the pith 
of Dioon and correctly interpreted them as belonging to the vascu- 
lar system of the peduncle. 
Sortms-LAvuBACH (4) traced the vascular supply of the peduncles 
in Stangeria paradoxa and Ceratozamia mexicana, and also noted 
the formation of phellogen in the leaf bases. 
In his Histologische Beitrige 111, SrRASBURGER (5) describes the 
histological structure of a large trunk of Cycas circinalis, and gives 
a critical discussion of the literature. 
In 1896, WorSDELL (6) made a thorough investigation of a large - 
trunk of Macrozamia Fraseri. This form has a well-developed 
system of vascular bundles in the pith, described as not being con- 
nected in any way with peduncles. There are also concentric zones 
of wood, as in Cycas, and these, WorsDELL (6) believes, are rem- 
nants of some ancient structure which consisted of rings or layers 
of concentric vascular strands. To him the structure recalls that 
of the Medullosa stem. 
From these accounts we get our conventional idea of the cycad 
stem, with its armor of leaf bases, thick cortex, narrow zone of wood, 
large pith, numerous medullary rays, and no growth rings. 
Investigation 
In September 1910 I was able to study in the field the adult 
trunks of Dioon edule and D. spinulosum, the study being facilitated 
by the active encouragement of Gov. Troporo A. Denesa, of the 
state of Vera Cruz. The field study was supplemented by notes 
and material from Mr. ALEXANDER M. Gaw, of the Bureau of 
Information, Jalapa, state of Vera Cruz. Abundant material of 
Dioon spinulosum, accompanied by notes, was sent to me by Mr. 
J. C. DENNIs, superintendent of the Hacienda de Joliet, near Tierra 
Blanca, but in the state of Oaxaca. I am glad to acknowledge My 
