CVi 



<TO 



LIBRARY 



NEW YOJ<K 

 BOTajv. 



THE VASCULAR ANATOMY OF THE SEEDLING OF 

 DIOON EDULE 



CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 1 19 



Reinhardt Thiessen 



(with PLATES xxih-xxix) 



This investigation was begun during the winter of 1906, the original 

 purpose being to clear up the confusing statements in reference to the 

 so-called girdling habit of the leaf trace. As the work progressed, 

 its scope became extended, until finally it included all of those ana- 

 tomical features of the seedling that have a bearing upon the relation- 

 ship of the Cycadales to the Cycadofilicales and Filicales. 



I wish to express my appreciation of the constant encouragement 

 received at all times from Dr. John M. Coulter, under whose direc- 

 tion the work was carried on; I also wish to thank Dr. C. J. Chamber- 

 lain for kindly furnishing the material. 



Historical 



The first work on Dioon edule was by Mettenius (4), who com- 

 pared it with Cycas revoluta, which was the special form investigated. 

 The methods of those days (1861) did not permit tracing the various 

 vascular bundles throughout their course. Sections were cut only 

 here and there, and the large number of bundles presented only a 

 very incomplete and vague idea to the investigator, resulting in com- 

 plete misapprehension. 



The picture of the leaf trace girdle as Mettenius drew it is in the 

 main as follows. A bundle in its course toward a leaf divides soon 

 after leaving the central cylinder, the two branches in turn soon 

 dividing. These branches and branchlets, in the main retaining their 

 radially ascending direction, but running at various angles, anastomose 

 with one another and with branches of neighboring bundles, and 

 finally unite with bundles which girdle the vascular cylinder. This 

 g ; rdle lies closest to the ring at a point diametrically opposite the leaf 

 base which its ends enter, each of which therefore traverses the cortex 

 through an arc of about qo°, gradually separating farther from it and 

 357] [Botanical Gazette, vol. 46 



