XLIIl] 



ANATOMY OP LEAVES 



141 



occur between the veins, but in the leaves of some species of 

 Podocarpus (fig. 695, D), externally indistinguishable from those 

 of Agathis, the ducts are below the veins^. Caution must be ex- 

 ercised in using the number of resin-ducts as a diagnostic character. 

 Schroeter^ draws attention to the occasional absence of ducts in 

 Picea excelsa leaves while in others 1 or 2 are present. In most 

 leaves there is some mechanical tissue immediately below the 

 epidermis either as scattered fibres or a continuous layer, but in 



Fig. 694. Leaves in transverse section. A, Cephalotaxus Fortunei. B, Torreya 

 myristica ; t, transfusion- tissue. C, Araucaria imbricaia ; i, transfusion-tissue 

 D, Pinus monophylla; e, endodermis. E, Cryplmneria japonica. F, Cedrua 

 Libani ; e, endodermis ; m, medullary ray. 



Taxus and Torreya there is none. The occurrence of branched 

 idioblasts is a striking feature in the mesophyll of Agathis, Arau- 

 caria, Sciadopitys, and Podocarpus. The infoldings of the walls 

 of the chlorenchyma are especially characteristic of Pine leaves- 

 (fig. 694, D) and they occur also in Cedrus (fig. 694, F), Pseudo- 

 larix and some other genera. The structure, extent, and position 

 of short isodiametric tracheids in association with the conducting 

 tissue is an important feature. This tissue, the elements of which 

 1 Seward and Ford (06) B. 2 Schroeter (97). 



