Tree ( Ginkgo bilob a, Z.). 133 
a few short elements of this type may occur on the centri¬ 
petal side of the foliar strand. 
The drawing shown in Fig. 59 represents the tracheids of 
a leaf-trace as seen in a tangential section through the cortex 
of a short shoot; the smaller group, x, may belong to an axillary 
bud. In Fig. 10 a short shoot is seen in radial longitudinal 
section ; the contraction of the pith has produced an appear¬ 
ance suggestive of a discoid pith like that of the Walnut or the 
extinct genus Cordaites. 
iv. Older branches . 
There are a few points in the structure of older branches 
worthy of note. The secondary phloem contains numerous 
thick-walled fibres with transverse or oblique cross-walls ; with 
these are associated parenchymatous cells and large sieve- 
tubes with sieve-plates in small groups on the radial walls (Fig. 
52). These several elements do not follow a regular or con¬ 
stant order of succession in a radial direction, but are variously 
arranged. In the secondary bast single swollen parenchymatous 
cells occur full of crystals ; similar sacs are found also in the 
cortex, pith, and medullary-ray tissues. In the autumn wood 
bordered pits are abundant on the tangential walls of the 
tracheids (Fig. 49), the pit-canals are often twisted, and appear 
as a cross when seen in surface-view. The bordered pits on 
the radial walls of the tracheids are often separated from one 
another by transverse radial bars 1 . The medullary rays are 
two to five cells deep, and their cells have simple oblique pits, 
but in some cases these appear to be bordered ; the branched 
medullary-ray cells of an old branch shown in Fig. 57 are un¬ 
usual in form, and pursue a somewhat obliquely radial course 2 
across the face of the tracheids. 
Strasburger 3 has described the anatomy of a Ginkgo stem 
fifty-eight years old ; it is unnecessary therefore to recapitulate 
the facts he records. 
1 Strasburger (’82), p. 42 , PI. III. 
3 Strasburger (’92), p. 45 . 
2 Cf. Russow (’83). 
