THE GYMNOSPERMAE : CYCADALES, ETC. 



733 



seeds, as do also the female branches which have been occasionally grafted 

 on to male trees. 



The name Ginkgo is something of an etymological puzzle. It is supposed to 

 be an erroneous copy of " Gin-ko," which is the Japanese equivalent of two 

 Chinese symbols meaning " silver fruit," a reference to its plum-like fruits. 



Anatomy of the Stem 



As in many Conifers there are both long and dwarf shoots, leaves being 

 borne spirally on both. There is in fact no hard and fast line between the 

 two types of shoot, and dwarf shoots may sometimes grow into long ones. 

 It is largely a question of the relative rates of growth. Normally the spurs 







"^ '^ t \f^^ Phloem 



Secretory canal 

 Periderm 



Secondary xylem 



Pith 



Fig. 736. — Ginkgo bilobo. Transverse section of a 

 two-year-old stem showing two annual rings in 

 the secondary wood. 



grow by very small increments to a length of 2 to 3 cm. and bear a cluster 

 of leaves at their ends. Occasionally they may branch, even precociously 

 within the wood of the axis from which they grow. 



Anatomically the stem is of XhePimis type (Fig. 736). The protoxylem is 

 formed of spiral elements which are exceptionally abundant, especially in 

 the spurs. The later-formed tracheids are all of the bordered-pit type, 

 with irregular pitting, often only in a single, loose row. There may also be 

 two rows, either opposite or alternate, and, in the secondary wood, the 

 thickenings known as Sanio's Rims are prominent between the pits. Here 

 and there also are trabeculae, crossing the interior of the tracheids. These 

 trabeculae have sometimes been confused with the Rims of Sanio, although 

 the latter are thickenings in the cell wall itself. 



