87 
The Anatomy of Ginkgo biloba. 
Text-fig. 16. Phloem is cross-hatched, tracheids cut transversely 
represented by series of dots, cut longitudinally by lines. Position of sterile 
ovule shown thus—X. 
A=bundle of fertile ovule ; B=bundle of sterile ovule : V=anomalous 
tissue; C=cambium ; H=“ horns”; T.L.=tracheids cut longitudinally; 
T.S. = tracheids cut transversely ; M=metaxylem ; K=crushed parenchyma 
between two phloems ; D=place where “horns” unite. PX=median plane 
of the pair of ovules. 
Transverse sections. 
1. Bundles in peduncle. 
2. Single bundle in pedicel—points of origin of anomalous tissue marked 
by two dots. 
3. 4. Lower part of collar—anomalous vascular tissue present. 
5. Commencement of approximation of “horns”—some tracheids cut 
longitudinally. 
6, 7, 8. Union of “ horns ’’—inverted vascular bundles splay outwards in 
the top of the collar. 
9. Single concentric bundle in base of ovule. 
10, 11. Splitting of bundle giving rise to two concentric bundles. 
ovule. The latter is usually small and in its passage up the peduncle 
gradually dwindles away and becomes lost in the mass of parenchyma 
and “ transfusion tracheids ” forming the bulk of the ground-tissue. 
In some cases in which the sterile ovule has developed to a rather 
greater extent this bundle can be traced as running definitely into 
it. It may be remarked that, as we proceed up towards the ovule, 
we find a gradually increasing number of “transfusion tracheids” 
intermingled with the ordinary parenchyma. These “ transfusion 
tracheids” are short and are reticulately thickened; they form a 
very characteristic feature of the sections. 
One of the bundles has now been disposed of and we pass to 
the consideration of the other, which will eventually give rise to 
the vascular system of the large fertile ovule. In a section taken 
at the base of the collar, just above the sterile ovule, this bundle 
exhibits normal collateral structure, the xylem facing towards the 
sterile ovule (Text-fig. 16, 2 ). On the outer edge of the phloem 
there is a fairly continuous layer of large, thick-walled, parenchy¬ 
matous elements stained with safranin. At one or two spots the 
ordinary parenchyma of the ground-tissue next to these large cells 
has an abnormal appearance. The cells are smaller, possess dense 
contents with well-marked nuclei, and appear to be rapidly dividing. 
The divisions at first take place irregularly in all directions, but a 
little higher up they begin to assume a definite tangential direction. 
The result is that at one or two places on the outer side of the 
main bundle, next the phloem, a dividing cambium is produced. 
This cambium gives rise to tracheids externally and to phloem 
internally, and several little vascular bundles with inverted 
