

ANATOMY 



249 











1 



























4 



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leaves of Juniper us , Thuya, &c., in which the stomata are more 

 abundant and more freely exposed than in ordinary foliage-leaves, 

 may similarly be connected with the need for rapid evaporation 

 through the stomata. In any case the arrangement, the torsion, 

 and the movements of leaves seem in some cases, and at some 

 periods, to promote the exposure of the assimilating or green side 

 of the leaf, and in other cases (or in the same cases at different 

 periods) to facilitate the exposure to light and heat of the stomate- 

 bearing surface. In all probability these differences are directly 

 connected with the assimilating process on the one hand, and 

 with the respiratory and exhaling processes on the other. 



Anatomy of the Leaf. — The complete discussion of anatomical 

 details lies without the scope of the present communication. 

 Information concerning them may be obtained from the ordinary 

 text-books and, in particular, from the memoirs cited in the 

 bibliographical list appended to this communication. 



Certain peculiarities of structure have, however, been proposed 

 as adjuncts to the discrimination and classification of the species, 

 and on that account demand some notice here. The epidermis 

 covering the adult leaves is represented in the cotyledons of many 

 species by a soft papular layer apparently destitute of cuticle. 

 In both cases the epiderm is perforated with stomata whose dis- 

 tribution and number afford useful aids in classification, while 

 their physiological significance is obviously a matter of importance. 

 In most cases (in all, so far as my own examination enables me 

 to say) the cotyledons have the stomata arranged on their upper- 

 most or innermost surface (see p. 239). In the adult leaves the 

 stomata are variously disposed on one or both surfaces, as is illus- 

 trated by the following list taken principally from Bertrand * : 



Stomata on lower surface chiefly : — Taxus, Tprreya, Cephalo- 

 taxus, Ginkgo, Saxe-Gothea, Podocarpus, J&umnopitys, Cunning- 

 namia, Agaihis, Cedrtis Libani, C. Deodara, Picea sitchensis, jezo- 



Dougl 

 bifida 



Q 



fi 



Stomata 



sibirica, homolepis, &c, &c. 



Chin 



on upper surface chiefly : — Juniperus, Athrotaxis 



Cedrus 



* 





Hookeriana, Abies nobilis, Davidiana, grandis, Regina 













P. 17. 



See also Hildeb 



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