35 o BOTANY OF THE LIVING PLANT 



shoot thus becomes intelligible, and comparison is facilitated with the 

 stem and fronds of the Pteridosperms, Cycads, and Ferns, in which 



Fig. 262. 

 Leaf of Sweet Chestnut (Castanea vesca), after Figuier. Here the fundamental 

 pinnate branching is shown by the veins, but the whole is condensed into a coherent 

 blade. 



the leaf is obviously a branched system (Chapter XXXI.). Rachis, 

 pinnae, and pinnules are in fact categories of parts of the shoot which 

 rank naturally with the category of the axis itself. They all represent 



Fig. 263. 



Stages of transition between scale and foliage leaf, in Ribes, after Figuier. 



correlative grades in the branching of the shoot as a whole. But the 

 distal branch-system of a leaf thus composed is so often greatly 



