BUDS AND LEAVES. 17 



and to the reproductive organs for their needs, receiving back merely 

 what is required for their sustenance and growth. 



BUDS AND LEAVES. 



We have already seen how the stem and branches elongate by the un- 

 folding of the bud, the expansion of leaves, and the lengthening of the 

 spaces between the latter, and have noted that the bud exists in the em- 

 bryo. From this time forward it always is the growing point of the plant. 

 Examined in vertical section, it is shown to be a collection of embry- 

 onic leaves, diminishing in size from without inward. In the growing 

 season the bud is green like the expanded leaves, though of a more tender 

 shade, but as the end of the season approaches the outer leaflets undergo 

 more or less change, including both color and texture, and are not unfre- 

 quently coated with resinous or gummy matters to protect them against 

 cold and moisture during the period of the plant's rest. Such altered 

 leaflets are termed scales. 



We have already seen how leaves are produced. We will now consider 

 their structure, varied forms, and functions. 



Leaves, like stems, consist of woody and cellular tissue, the former col- 

 lected in bundles or fibres which form a skeleton whose interstices are 

 filled up with the latter. 



Upon the form of the skeleton, of course, depends the shape and gen- 

 eral character of the leaf. 



The larger and more prominent fibres of the skeleton are termed 

 veins, the smaller ones vein lets. In leaves having a large central vein, 

 with less prominent lateral branches, the central one is termed the mid" 

 vein or mid-rib. Indeed, in botanical descriptions the prominent fibres 

 of the leaf-skeleton are spoken of as veins, ribs, or nerves indiscrimi- 

 nately, as for example, a leaf is feather -veined, strongly ribbed, or triple- 

 nerved. Little confusion, however, need arise from this misuse of terms if 

 the student but remember that though these fibres bear some analogy to 

 veins and ribs, they bear none whatever to nerves. 



A leaf may commonly be distinguished into two parts : an expanded 

 portion, termed the lamina or blade, and a stalk by which this is at- 

 tached to the stem, termed the petiole or footstalk. In case there be 

 no petiole, the blade being attached directly to the stem, the leaf is said 

 to be sessile. 



Through the petiole, if there be one, or, in its absence, directly into 

 the base of the blade, pass the woody fibres whose ramifications make up 

 the leaf-skeleton. The manner in which the veins ramify is termed the 

 venation of the leaf. 



In endogenous plants these fibres commonly divide at or near the base 

 of the blade into a number of nearly equal branches, which pursue a parnl- 



