THE GYMNOSPERMAE : CYCADALES, ETC. 



737 



Although the mature parts of Ginkgo are almost completely devoid of 

 hairs, the petioles of young leaves and the bud scales are densely hairy, as in 

 Cycos, and some hairs remain at the base of the petiole even in the mature 

 leaf. 



Anatomy of the Root 



There is little about the root structure that is different from that in the 

 Conifers, except the very early differentiation of tissues at the apex. There 

 is a persistent tap root, and the vascular structure of the young root is usually 

 diarch. The details of the vascular tissues are closely similar to those of the 

 stem. 



The Male Strobilus 



As has been already mentioned, Ginkgo is dioecious. The male tree is said 

 to be more upright in growth than the female, but it is doubtful whether 





Fig. 740. — Ginkgo biloba. Branches with spurs bearing \oung leaves and male strobili. 



{From a photograph by Mr E. Cahen.) 



this is alwavs so. The male strobili are borne in the axils of leaves on the 

 spurs, about half a dozen on each spur, so that the aggregate number for the 

 tree is enormous (Fig. 740). They are about i in. in length and consist of a 

 slender axis bearing closely set sporophylls in spiral order and without bracts. 

 Each sporophyll normally bears two pendant sporangia at its apex, but three 

 or four are occasionally present (Fig. 741). Above the sporangia is a promi- 

 nent " hump " of sterile tissue containing a large mutilage cavity, and it 

 has been suggested that this represents an additional sterilized sporangium. 



