POLYXYLIC STEM OF CYCAS MEDIA 



CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 252 



Ward L Miller 

 (with eleven FIGLTIES) 



The question which lends particular interest to the polyxylic 

 situation in 4 of the cycad genera {Cycas, Macrozamia, Ence- 

 phalartos, and Bowenia) is whether or not the separate, concentric, 

 vascular cylinders all originate with the differentiation of pro- 

 cambium strands in the plerome cylinder, and whether or not 

 true protoxylem and protophloem are formed in every or in any 

 instance. If protoxylem and protophloem are formed, are they 

 or are they not orthodox in their detailed structures, and what is 

 their condition in the older parts of the stem ? 



It is the purpose of this investigation to discover the exact 

 origin and behavior of the different cambiums which develop the 

 separate vascular cylinders, and to formulate some definite con- 

 clusions regarding the vascular elements which will leave the 

 matter of this unusual method of secondary growth more clearly 

 understood. 



Historical 



Although research among the cycads has been comparatively 

 limited by lack of suitable material for study, several accounts 

 have been published which deal more or less directly with the 

 present problem. During an investigation of Cycas stamens is in 

 1885, CoNSTANTiN and MoROT' concluded that the cambium of 

 each supernumerary zone, laid down outside the first or normal 

 cylinder, originated in the pericycle of the cylinder next inside. 



In 1896 WoRDSELL^ published an account of the polyxylic 

 stem of Macrozamia. In this particular genus he found the corti- 



■ CoNSTANTrN, J., and Morot, L., Sur I'origine des faisceaux libero-ligneux super- 

 numeraires dans la tige des Cycadees. Bull. Soc. Bot. France 32:173. 1885. 



^WoRDSELL, W. C, Anatomy of stem of Macrozamia compared with that of 

 other genera of Cycadeae. Ann. Botany 10:601-620. 1896. 



Botanical Gazette, vol. 68] [20S 



