286 



PHOTOSYNTHETIC SYSTEM 



plate the palisade-cells bend round towards the adjacent bundle-sheath, 

 while above the air-passages they abut against the intermediary tissue ; 

 the latter consists of rows of transversely elongated cells poorly provided 

 with chlorophyll, and effects a connection between the parenchymatous 

 sheaths of adjoining vascular bundles. The photosynthetic tissue on the 

 abaxial side of the leaf is very similar, except that the subepidermal cells 

 are not of the palisade-type. On collating the anatomical data obtained 



Fin. 116. 



Palisade-tissue in various leaves. A. Asplenium liuta muraria, adaxial side of leaf ; 

 a, funnel-shaped collecting-cells. B. Asphnthlvx Villarsii. T.S. xl06. C. Cryptomeria 

 elegans. X(>5. Photosynthetic system of the laminated type. I). Aspidium Sieboldi. 

 T.S. k, collecting cells. E. Asplenium Belangeri, fertile portion of pinna. Meso- 

 phyll only comprises two layers, viz. an adaxial layer of funnel-cells and an abaxial 

 layer of spongy-parenchyma. 



from the transverse and longitudinal sections, one realises that the whole 

 construction of the photosynthetic system is such as to ensure the 

 transference of synthetic products to the main conducting channels by 

 the shortest route, thus clearly revealing the dominating influence of the 

 principle of expeditious translocation. 



The general structure of the ordinary dorsiventral Dicotyledonous 

 leaf has been repeatedly discussed, since its first thorough investigation 

 at the hands of Brogniart and Treviranus. In this case the upper 

 epidermis is always underlain by a one- to many-layered palisade-tissue, 

 which is usually very loose in texture. The originally prismatic 

 photosynthetic elements show a marked inclination to become cylin- 

 drical, so that the radial walls are particularly liable to separate from 



