116 Seward and Gowan .— The Maidenhair 
and the larger leaf is also slightly bilobed. The cotyledons 
appear to be united at the apex, but each retains a distinct 
epidermal layer, so that they are not strictly connate. In the 
upper part of the cotyledons there are two small vascular 
bundles, one in each lobe, containing three to four xylem- 
elements; below the point of splitting each cotyledon is tra¬ 
versed by a single arc-shaped bundle consisting of about nine 
tracheids. In the peripheral part of the cotyledons secretory 
canals are seen in process of development. The stalk of 
a cotyledon is crescent-shaped in transverse section, and is 
traversed by a single vascular bundle of similar form. The 
epidermis is well defined, the outer walls being slightly thick¬ 
ened ; numerous secretory canals occur in the ground-tissue, 
and are especially abundant on the convex side of the petiole. 
As Worsdell 1 has shown, the vascular bundle is mesarch in 
structure ; the xylem-elements are disposed in fairly regular 
radial rows, separated by comparatively broad medullary-ray 
cells; the protophloem forms a peripheral band of crushed 
tissue and a few secretory cells occur immediately beyond it. 
Several elements of centripetal xylem are met with on the 
inner side of the protoxylem. Transfusion-tracheids are few 
in number, but occasionally a single clump may be noticed on 
one side of the bundle. 
Ginkgo has been described as peculiar among Conifers in 
possessing hypogeal cotyledons 2 . 
B. Scale-leaves. 
Plate IX, Figs. 31-36. The outermost scale-leaves from the 
terminal bud of a long shoot consist in the upper portion 
entirely of suberized tissue; in the next scale-leaves three or 
four peripheral layers are composed of cork cells, and in some 
of the bud-scales the elements of the cork-phellogen become 
themselves suberized 3 . Two vascular bundles are present 
in each bud-scale, containing several centripetal xylem-ele¬ 
ments ; a few transfusion-tracheids occur on each side of the 
1 Worsdell (’ 97 ), p. 305. 2 Tubeuf (’ 91 ), p. 96. 
: Cf. Haberlandt (’ 96 ), p. 123. 
