442 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1938 



PART I 

 GINKGO BILOBA 



Ginkgo, like the larch, is one of the few naked-seeded (Gymno- 

 sperm) trees that is deciduous; it reaches well over a hundred feet in 

 height: the branches are spreading or steeply ascending. In the 

 autumn the leaves assume an attractive golden color before falling. 

 In shape and venation the foliage is unlike that of any other tree; 

 it is fan-shaped or triangular and varies considerably in size and 

 shape. The specific name biloba was chosen because in many, though 

 by no means all, leaves the blade is divided by a median V-shaped 

 depression into two symmetrical halves. Leaves vary from about 1 

 inch to 2 or 3 inches in depth, and from 1 to 3 inches in breadth; 

 they may reach a breadth of 6 inches, but this is exceptional. The 

 slender leaf-stalk is IK or as much as 2 inches long. The lower margin 

 of the blade may be almost straight and at right-angles to the stalk, 

 or not infrequently in small leaves the outline is triangular, the two 

 sides converging to the base: occasionally the lower margin has the 

 form of a double ogee curve. The upper edge is rounded, entire, ir- 

 regularly undulate, or bilobed. In some leaves, especially those on 

 vigorous yoimg shoots, the blade is often dissected by V-shaped de- 

 pressions into four or more wedge-shaped segments. The deeply cut 

 leaves with several cuneate lobes are reminiscent of the foliage of 

 many extinct species. The range in size and shape of the foliage 

 of the living species adds considerably to the difficulty of deciding 

 whether or not certain fossil leaves should be regarded as specifically 

 identical with Ginkgo biloba, or indeed one with another. Accurate 

 comparison is impossible without the aid of supplementary evidence 

 from structural features. Forked veins radiate through the leaf from 

 the lower margin: the venation is very similar to that of the leaflets 

 of a maidenhair fern (Adiantum). Two strands of conducting tissue 

 pass from the stem up the leaf-stalk and branches from them form 

 the spreading and forked veins. Here and there between the veins 

 short tracts of secretory cells are easily recognizable as translucent 

 patches when a leaf is seen in transmitted light, or as dark patches 

 by reflected light. Similar secretory tracts are an almost constant 

 character in the fossil leaves. 



The leaves are borne on two kinds of shoot: long shoots which grow 

 with relative rapidity and determine the shape of the tree; also short 

 and very slow-growing shoots. On long shoots the leaves are scattered 

 and spirally disposed, while on the short shoots about six or fewer 

 are borne as a cluster at the tip. The surface of a dwarf or short 

 shoot is covered with crowded scars left by leaves of past years. 

 Special attention is called to the short foliage-shoots because they 



