. THE VASCULAR ANATOMY OF THE SEEDLING OF 
DIOON EDULE 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY IIQ 
REINHARDT THIESSEN 
(WITH PLATES XXIII-XXIX) 
This investigation was begun durin g 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 
Teceived at all times from Dr. Joun M. Coutter, under whose direc- 
tion the work was carried on ; Lalso wish to thank Dr. C. J. CHAMBER- 
LAIN for kindly furnishing the material. 
Historical : 
The first work on Dioon edule was by Metrentus (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 METTENIWS 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 
mith one another and with branches of neighboring bundles, and 
nally unite with bundles which girdle the vascular cylinder. This 
Sirdle lies closest to the ring at a point diametrically opposite the leaf 
€ which its ends enter, each of which therefore traverses the cortex 
through an arc of about go°, gradually separating farther from it and 
357] [Botanical Gazette, vol. 46 
