THE LEA VES. 



139 



the basal growth of a single pair of persistent secondary 

 leaves is continued throughout the long life of the plant, 

 while the tips die and are frayed out. 



173. Production of the other members. — Leaves give rise 

 under certain conditions to roots or to shoots. The number 

 of plants, however, in which this occurs is comparatively 



Fig, 166. — De\-elopment of the pinnately compound leaf of the locust {Robi>iia Pseuds 

 acacui). A, j'OQng stage, sha\\'ing on one flank the first lateral growing-point u, 

 which is to produce the lowest leaflet, A, an older stage with the fifth growing-point 

 X jtist showing, A sbcth is still to be developed, I'he hairs in A and [• are on the 

 back (under side) of the leaf, and drop off early, C, nearly mature leaf. A, B, 

 magnified ; c, about I natural siiLe, — After Frank, 



limited. Roots arise from leaves in precisely the same way 

 as lateral roots arise from stems {'•[ 95), that is, they are en- 

 dogenous in their origin, and develop always near the surface 

 of the steles. 



Wlien a leaf produces a shoot, it is from the epidermis or 

 from the green tissue underlying it, never from the steles. 

 Shoots thus arise from the part of the leaf corresponding to 

 that from which branches arise upon the piarent shoot. 



174. Secondary ciianges. — Leaves, like stems and roots, 

 undergo certain secondarv chanijes, but these are neither so 



