Tree (Ginkgo biloba , Li). 115 
long shoots bearing scattered leaves with a phyllotaxis of 
two-fifths. 
Flowers dioecious. The male flowers, which occur in the 
axil of scale-leaves, have the form of a stalked central axis 
bearing scattered loosely disposed stamens ; each stamen con¬ 
sists of a slender filament terminating in a very small apical 
scale, and usually two, sometimes three or four, elliptical pollen- 
sacs which open by longitudinal dehiscence. The pollen- 
grains develop a rudimentary prothallus consisting of a few 
cells, and before fertilization two large spirally coiled multi- 
ciliate spermatozoids are produced from the generative nuclei 
in the pollen-tube. The female flowers usually have the form 
of a long peduncle bearing two terminal elliptical ovules 
enclosed at the base by a collar-like envelope representing a 
reduced carpellary leaf. Abnormal female flowers, possessing 
more than two ovules, are not infrequently met with. Each 
ovule consists of a nucellus enclosed by a single integu¬ 
ment, which in the ripe seed forms a thick fleshy covering 
surrounding a hard woody shell; the nucellus possesses a well- 
marked pollen-chamber, and in the mature ovule the greater 
part of the nucellar tissue is reduced to a thin papery layer 
enclosing a large embryo-sac which usually contains two 
archegonia. After fertilization, which may occur either before 
or after the ovule has fallen from the tree, the egg-cell develops 
directly into an embryo with two cotyledons. 
The secondary wood of Ginkgo is composed of tracheids 
with numerous bordered pits on the radial and not un¬ 
commonly on the tangential walls. Resin ducts occur in 
abundance, both in the pith and in the cortical tissues. 
I. Leaves. 
A. Cotyledons. 
The embryo shown in PL IX, Fig. 44, removed from the 
endosperm of a germinating seed, illustrates the unequal length 
of the two cotyledons. The smaller seed-leaf is divided into 
two lobes by a slit extending through about half its length, 
