LEAVES. 



19 



renchymatous layer, the cells of which are different in 

 form in the layer next the under epidermis, to what 

 they are in those beneath the upper ; aud between these 

 two layers is situated the diploe, in the cells of whose 

 tissue is contained organic and colouring matter. 



101. The petiole consists of two larger fascicles of fibro- 

 vascular tissue, one of which is continuous with the me- 

 dullary sheath, the other being the returned and collected 

 fibres .from the lower surface of the lamina, is continuous 

 with the bark. They are covered by epidermis. 



102. The development of the petiole is sometimes so 

 abnormal as to simulate in appearance the lamina of a 

 leaf, or else to give rise to structure of more particular 

 configuration. 



103. Phyllodium is the term applied to such a plane 



development of the petiole, as at (a). 



104. Ascidium to such formations as 

 the pitcher of Nepenthes (6).* 



105. When a petiole at once ex- 

 pands into a lamina without subdividing 

 (fig. 11.), the leaf is called simple ; when 

 the petiole subdivides into secondary pe- 

 tioles, each bearing separate laminae, the 

 leaf is compound. 



Fig. 13. 



Fig. 12, 



Pinnate. 



Ternate. 



* From some late observations of Morren, it would seem that the 

 pitcher is to be considered rather as a modified lamina than petiole. 



