Tree (Ginkgo biloba , Li). 117 
bundle, and on the centripetal side of the protoxylem an arc 
of secretory cells extends round the protophloem, and three or 
four secretory sacs traverse the ground-tissue. The scale- 
leaves represented in Figs. 31-36, taken from the bud of a 
seedling 20 cm. in height, illustrate a gradual transition from 
a small triangular scale, of which the tissues are almost com¬ 
pletely suberized, to longer scale-leaves, in which the cork 
tissue is confined to the apex, passing gradually into still 
longer and narrower leaves, in which a small emarginate 
lamina is differentiated from a broad and flat stalk. The 
expanded lower portions of the scale-leaves bear numerous 
hairs, which form a distinct woolly fringe to the petiole and are 
abundant on the small lamina. The enlarged drawings in 
Figs. 39 and 40 show more clearly the conspicuous hairs on 
the broad petiole and small laminar portion of a scale-leaf. 
Somewhat similar hairs, but less strongly developed, occur on 
the cotyledons of Pinus Pinea , L. 
C. Foliage-leaves. 
The manner of development of the foliage-leaves has been 
dealt with by Fankhauser 1 in a paper published in 1882. 
He describes the first appearance of a leaf as a transverse 
protuberance embracing about two-fifths of the circumference 
of the stem-apex; this swelling soon exhibits a distinct emar- 
gination which becomes a fairly deep median incision. The 
lamina is bent over the apex, and its margin is strongly in- 
rolled ; for a time the growth is marginal, but this is succeeded 
by intercalary meristematic activity. As Fankhauser pointed 
out, the abundance of long trichomes affords an interesting 
peculiarity of young Ginkgo leaves 2 : on some of the small 
scale-leaves hairs are particularly abundant, and a few occur 
also on the lamina of the young foliage-leaves, but they are 
more numerous on the leaf-stalk, which is at first almost 
covered with them, especially on the inner face ; in older leaves 
the hairs are confined to the base of the petiole, and are visible 
1 Fankhauser (’ 82 ), p. 5. 
a Ibid. (’82), p. 7, Figs. 16-18, 22 and 23. 
