



ANATOMY, AND LIFE-HISTORY OF THE CONIFERtE. 



265 

















































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or concrescent leaves, and which hare nearly the same structure as 

 the free leaves. Thus a cross section of the concrescent appressed 

 leaf of a Juniper shows the dorsal or outer surface to be convex 

 with a central depression. The epidermis is without stomata, next 

 to it is a layer of hypoderm-cells, followed by palisade-cells filled 

 with chlorophyll, and these by loose parenchyma, through the 

 centre of which runs the fibro-vascular bundle. Near the 

 upper or inner, more or less appressed surface chlorophyll-cells 

 again appear, but less regular in shape and dimensions than 

 those beneath. There is no hypoderm, and stomata are wanting 

 except in a central spot marked by glaucous bloom at the base 

 of the leaf. In these leaves, then, the palisade-cells are on the 

 dorsal surface, which, owing to the position of the leaf, is most 

 exposed to the light, and the stomata are on the upper surface. 



The relatively free leaves have essentially the same structure. 

 If the bud, say of a Juniper or a Cryptomeria, be examined in 

 the young state, the three leaves of which it consists will be 

 found free at the base. Hitherto growth and developmental 

 change in axis and leaf have been uniform and proportionate ; 

 but after a short time the basal portions are uplifted with the 

 stem in its upward growth, so that the term " decurrent " really 

 conveys an idea the exact reverse of the truth. 



It is moreover obvious that, in Juniperus, Thuya, Dacrydium, 

 &c., the concrescent leaves are more especially (but not quite 

 exclusively) found on the more rapidly growing shoots, those 

 which may be conveniently called, in gardener's phraseology, 

 "extension shoots," to distinguish them from the more slow- 

 growing framework shoots, and on which the leaves are free at 

 the base owing to the more uniform and regular progress of 

 development. In a young plant of Frenela, preserved in the 

 herbarium of the British Museum, the cauline leaves are all free, 

 acicular, and spreading, but when the stem commences to branch 

 the leaves are seen to be concrescent. Meehan # considers that 

 this concrescence, or adnation as he terms it, is specially charac- 

 teristic of vigour, while free leaves indicate a state of weakness 

 and arrested growth ; and in a sense this is true, for it is gene- 

 ally on the rapidly growing extension shoots that the concrescent 











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Proc. Acad. Nat. Sc. Philadelphia, 1868, p. 181 ; 1872, p. 33 ; and 

 ■Proc. Amer. Soc. Adr. Science (1868), Chicago ; see also Pasquale, ' Delia 

 eterophyllia nel Cuprums funebris,' Napoli, 1872. 









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