30 



HORTICULTURE FOR SCHOOLS 



lished. It is possible that at some future time methods of 

 pruning, culture, and irrigation may be devised which will 

 overcome alternate bearing in fruit-trees. 



45. The leaves. Leaves generally have two parts, the 

 blade and the stalk (petiole). Sometimes smaller leaf -like 

 structures, called stipules, are borne at the base of the 

 petiole, as in the leaves of many varieties of apples. When 

 leaves have no petioles, they are said to be sessile. When 



apples have 

 been borne by the spur 

 and this year's apple is 

 still on the twig. 



the blade of a leaf is single, it is simple as in the plum or 

 cherry, and when the blade is divided into a number of small 

 leaves, as in the carrot, it is compound. Leaves may be 

 parallel-veined as in the grasses, or netted-veined as in the 

 apple or peach. Netted-veined leaves grow on exogenous 

 stems, and parallel-veined leaves on endogenous stems. 

 Leaves vary greatly in size, shape, thickness, and markings. 



46. Structure of leaves. Vascular bundles run up from 

 the stem through the petiole and into the tissues of the blade 

 of the leaf, subdividing and becoming smaller until they end 

 in a few rows of cells. The vascular bundles carry water and 

 food material in solution to and fro, and also strengthen the 

 leaves. 



The structure of a leaf is best shown by a cross-section dia- 

 gram. The upper and lower surfaces of the leaves are covered 



