CHAPTER V 



GINKGOALES 

 Ginkgo biloba is the only living representative of a gymnosperm 

 phylum that was well represented during the Mesozoic. It is almost 

 unknown in the wild state, the only reports of its occurrence having 

 come from travelers in the forest regions of western and southwestern 

 China (28). Its extensive cultivation, however, first in China and 

 Japan, and later in Europe and in the United States, has made it 

 very accessible. It was long included among the Taxaceae as an 

 exceptional member, and only since 1897 has it been set apart as 

 representing a group coordinate with Coniferales and Cycadales, and 

 all subsequent morphological investigation has confirmed this position. 

 The appropriate but antedated name Salishuria adiantifolia has 

 sometimes been used for the plant, and now and then an additional 

 species or two have been segregated, but the generic name Ginkgo 

 must be accepted, and the segregates have had little recognition. 



1. The vegetative organs 



The tree has the general habit of a conifer, with central shaft and 

 wide-spreading branches (fig. 211), and attains a height of more than 

 30 m., with a diameter exceeding 1.5m. The deciduous foliage 

 leaves are very characteristic in form and venation, and are so sug- 

 gestive of the leaves of Adiantum that the common name "maiden- 

 hair tree" seems appropriate. The petiole is long and slender, the 

 blade is broadly wedge-shaped and variously lobed, and the venation 

 is conspicuously dichotomous (fig. 212). 



The branches are dimorphic; one kind being long shoots that 

 elongate rapidly and bear scattered leaves; the other being the 

 numerous dwarf shoots that elongate very slowly and bear few leaves 

 in a cluster. The dwarf shoot elongates slightly each year, bearing 

 a terminal group of leaves, and the older portion is covered with leaf 

 scars of previous years. After several years a dwarf shoot may become 

 a long shoot, bearing scattered leaves; and then it may resume the 

 slow growth of the dwarf shoot again; and in some cases it may branch 

 (28). 



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