GIXKGOALES 



37 



28, 29). There is great variability, however, both in size and 



amount of lobing. 



The development of the foliage leaf has been described by 



Fankhauser. 6 It is at first a protuberance embracing two fifths 



of the circumference at the stem 



apex. Soon a distinct emargina- 



tion is developed which becomes 



a deep incision. During devel- 



opment the blade is bent over at 



the apex and the margins are 



strongly inrolled. The leaves, 



especially when young, are not 



merely deeply two-lobed, but 



each lobe is variously toothed 



or divided. 



In anatomical characters the 



leaf resembles those of Cycads. 



There is developed an evident 



but not very thick cuticle. The 



stomata are restricted to the 



lower surface, the guard cells 



being somewhat below the level 



of the epidermis. A palisade 



tissue is evident, but somewhat irregular. A transfusion tissue, 



such as was described under the Cycads, appears also in the 



leaves of Gink- 

 go, cells of the 

 inner mesophyll 

 elongating in a 

 plane parallel 

 with the leaf 

 surface and de- 

 veloping numer- 

 ous and promi- 

 nent intercellu- 

 lar spaces. 



I M f* 



FIG. 28. Ginhgo biloba, a cluster of 

 leaves and a mature seed. 



FIG. ^. Ginl-no biloba, a single leaf, showing venation. 



are deciduous, a 



rare habit among Gymnosperms, being displayed in Conifers 

 only by Larix, Taxodium disticlium, and Glyptostrobus. 



