240 Worsdell. — The Vascular Structure of 
has become, as a result of the sporangiferous function, much 
more highly modified from the primitive type than that of the 
foliage-leaves, this special function influencing more or less 
all parts of the vascular system. But though this modifica- 
tion in structure has taken place, it has not obscured, to such 
an extent as in the foliage-leaves, the primitive character of 
the organ which, either in the form of concentric or partially 
concentric strands, of irregular orientation and arrangement 
of the bundles, of great variability in size of the latter, or of 
a tendency to abortion of certain of the more primitive parts 
of the vascular system, appears over and over again, in one 
place or another, throughout all the genera investigated. 
I desire to express my obligation to Dr. D. H. Scott for all 
the assistance and the numerous criticisms which he has, as 
usual, so kindly afforded me. 
EXPLANATION OF FIGURES IN PLATES 
XVII AND XVIII. 
Illustrating Mr. Worsdell’s paper on the Cycadaceae. 
The following are the abbreviations used: — ph. phloem; ph}. ventral phloem; 
x 1 . centrifugal xylem ; x l . centripetal xylem ; px. protoxylem ; tf transfusion-tissue ; 
pb. bundle from peduncle ; fb. foliar bundle ; ped. peduncle ; bs. barren sporophyll ; 
sph. sporophyll (fertile) ; sp. sporangium ; Im. lamina ; st. stalk. 
Fig. 1. Cycas circinalis , L. Diagrammatic transverse view of the arrangement 
of the vascular bundles in the stalk of the 9 sporophyll. x 35. 
Fig. 2. Cycas circinalis , L. Transverse section of a strand from the stalk of 
the 9 sporophyll. x 65. 
Fig* 3 * Cycas circinalis , L. Transverse section of a bundle from the lamina of 
the ? sporophyll. x 100. 
Fig. 4. Cycas revoluta , Thunb. Transverse section of a concentric strand 
about to enter the megasporangium, x 65. 
Fig. 5. Stangeria paradoxa , Th. Moore. Diagram of the vascular bundle-system 
of the 9 sporophyll. 
Fig. 6. Stangeria paradoxa , Th. Moore. Diagrammatic transverse view of the 
arrangement of the vascular bundles in the stalk of the 9 sporophyll. x 35. 
