

Reprinted for private circulation from 

 The Botanical Gazette, Vol. LXX, No. 2, August 1920 



STEM ANATOMY OF DIOON SPINULOSUM 



CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 270 



LaDema M. Langdon 

 (WITH PLATES XV-XVII AND FOUR FIGURES) 



Introduction 



Investigations dealing with the minute anatomical structure 

 of the adult cycad stem have become very numerous and more or 

 less thorough for all of the genera and many of the species, with the 

 exception of the great Mexican representative, Dioon spinulosum. 

 This unique and interesting species was first but inadequately 

 described by Eichler (6) in 1883, and by Dyer (5) in 1885. The 

 first extensive account of its general field characters, size, external 

 structure, and distribution was by Chamberlain (i) in 1909. 

 A later article (2) by the same author gives a full and careful 

 description of the macroscopic structure of adult stems of Dioon 

 spinulosum, D. edule, Ceratozamia mexicana, and Zamia fioridana, 

 particular attention being given to D. spinulosum. Special study 

 is made of the growth rings, reported here for the first time in 

 cycads, and of the medullary bundles which constitute the vascular 

 system of the cones, and which are called cone domes, because of 

 the domelike arrangement of these strands with the peduncle of 

 the cone at their apex. The histological characters of the trunk, 

 its growth rings, the thick-walled fibers of the phloem, and the 

 structure of the xylem elements the author considers remarkably 

 similar to the corresponding structures of Cycadeoidea. 



The embryo and seedling of D. spinulosum have been studied 

 recently by Sister Helen Angela (4) , and found in the arrangement 

 and orientation of the vascular strands in the cotyledons, hypocotyl, 

 stem, and leaves to differ in no marked degree from the usual 

 cycad arrangement. Features particularly worthy of note in con- 

 nection with the girdling habit, as this investigator has traced it 

 r- from macerated seedling stems, is that each leaf is supplied with 

 o*> five strands arising from cauline bundles situated in different parts 



cvj Botanical Gazette, vol. 70] [no 



