STEM ANATOMY OF DIOON SPINULOSUM 



CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 270 



LaDema M. Lang don 



(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 spinnlosum. 

 This unique and interesting species was first but inadequately 

 described by Eichler (6) in 1883, an d 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 jioridana. 



P 



Special study 



made 



■ 



cycads, and of the medullary bundles which constitute the vascular 



domes 



domelike 



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



grow 



structure of the xylem elements the author considers remarkabl) 

 similar to the corresponding structures of Cycadeoidea. 



P 



H 



ement 



hyp 



stem, and leaves 



marked deeree from the usual 



cycad arrangement. Features particularly worthy of note in con- 

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

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

 five strands arising from cauline bundles situated in different parts 



Botanical Gazette, vol. 70] 



[no 



^ 



A 



