190 



MORPHOLOGY OF GYMNOSPERMS 



the leaf is suddenly resumed, the contrast between the entire leaves 

 of the dwarf shoot and the lobed leaves of the new long shoot being 



quite marked (fig. 216). The 



^ ^ ^^^m^ deep lobing is a juvenile 



^^^K ^!^^F character, and by many would 



^\ ^ \V be regarded as an illustration 



^^^ ^^ifc ,Ax °^ recapitulation. 



^^^""^^^N. ^1 \ During development the 



^^ I ^ \ blade is bent over at the 



•' ■ apex and the margins are 



strongly inrolled (8). The 

 young leaves develop abun- 

 dant hairs, especially on the 

 petiole; and the hairs are 

 numerous on the scale leaves, 

 forming a distinct woolly 

 fringe to the petiole (28). 

 The deciduous habit is a very 

 rare one among gymnosperms, 

 being shared with Ginkgo only 

 by the coniferous genera Larix, 

 Taxodium, and Glyptostrohus. 

 In anatomical structure the 

 leaves of Ginkgo resemble in 

 general those of Cycadales. 

 There is an evident but not 

 very thick cuticle; the stomata are mostly restricted to the abaxial 

 surface, the guard cells being somewhat below the level of the epi- 

 dermis; there is a distinct paHsade tissue in the larger leaves, but not 

 in the leaves of the dwarf branches; and between the veins the very 

 loose inner mesophyll cells are elongated parallel with the plane of 

 the leaf surface. 



2. The spore-producing members 



The strobili of Ginkgo are not only monosporangiate, but the plants 

 are also dioecious, as in the Cycadales. Neither kind of strobilus 

 is bracteate, as is usual among gymnosperms; and the o\ailate 

 strobilus has given rise to much discussion. 



Fig. 215. — Ginkgo biloba: seedlings 

 showing deeply bilobed leaves; the seed 

 and cotyledons have not yet fallen off. 



