1908] THIESSEN—DIOON EDULE 377 
at points not definitely located but well-distributed; two strands of each 
organ leave the cylinder approximately on the same side as the leaf for 
which they are destined, and run more or less directly through the 
cortex into the central or abaxial part of the petiole without branch- 
ing; while the other two strands of each organ leave the cylinder 
approximately on the opposite side and describe a wide curve around 
it, the one in one direction and the other in the other, and finally 
ascend in the dorsal or adaxial part of the petiole, branching repeat- 
edly. The girdle on the side toward which the spiral may be said to 
turn is generally the longer one. 
5- When the cotyledonary vascular strands leave the vascular 
cylinder they are endarch, gradually become mesarch in their upward 
Course, and finally approach the exarch condition. 
6. The foliar vascular strands also are endarch at their separation 
from the vascular cylinder, and in their upward course become 
Mesarch and finally exarch. In the very young leaf this transition 
extends through the whole base and petiole uniformly; but in the 
Adult leaf it is comparatively rapid through the base up to the lower 
Part of the petiole, where only a few centrifugal elements remain, and 
Which remain uniform until in the rachis, where the transition is com- 
Pleted, so that in the pinna only centripetal xylem is left. 
7 In the lower stretches of the foliar strands a considerable 
amount of the centrifugal wood is primary xylem. 
: 8. In the foliar strands of the embryo and seedling, the xylem 
issue, so far as developed, from below upward passes from an inner 
to a central position in reference to the whole bundle. 
9. The girdle is established very early, and is horizontal from the 
ing. 
Untrep Starters GEOLOGICAL SURVEY 
Wasuincton, D. C. 
: LITERATURE CITED 
* Von Mont, Huco, Ueber den Bau des Cycadeen-Stammes und sein Ver- 
hiltniss zy dem Stamme der Coniferen und Baumfarn, Abhandl. Kgl. Bay. 
nt Wiss. 1: 399-442. pls. 18-20. 1832. : 
“ TEN, G., Organographische Betrachtung der Zamia muricata Willd. 
Abhandl. Kgl. Akad. Wiss. Berlin 1856:193-219. pls. 1-3. 
