THE STRUCTUEE OF THE LEAF 395 



underlying the epidermis. The formation of cork is, however, 

 very rare in leaves. 



The structure of the outer floral leaves differs but slightly 

 from that of the foliage leaves described. Bracts and sepals are 

 only very little modified, the chief difference being the general 

 absence of sclerenchyma. The upper as well as the lower epi- 

 dermis, as a rule, contains stomata. When the sepals are fused 

 to form a gamosepalous calyx, sometimes the fibro-vascular 

 bundles of the separate leaves anastomose freely, sometimes 

 they remain independent. 



The petals are generally more altered ; the epidermis is 

 often papillose and its cells filled with various colouring 

 matters. There is no differentiation of the mesophyll into 

 palisade and spongy parenchyma, and the vascular bundles are 

 much reduced. 



The structure of the sporophylls will be best discussed in the 

 succeeding section. 



