152 LEAFY SURFACE OF PETIOLES. DISTRIBUTION OF VEINS. 



the leafy foot-stalk. In all these, the amount of expansion 

 of the petiole bears a precisely inverse proportion to that of the 



FIG. 61. BRANCH OF NEW HOLLAND ACACIA. 



leaf; the former replacing the latter, when it is unfit to perform 

 its functions. 



229. The blade of the leaf is composed of the expanded veins 

 or nerves proceeding from the petiole, the interstices between 

 which are filled up with cellular tissue,, and the whole covered 

 with cuticle. The mode in which these veins are distributed 

 is very characteristic of the principal divisions of the vegetable 

 kingdom. Thus, in the CRYPTOGAMIA, wherever true woody veins 



