78 PRINCIPLES OF PLANT CULTURE 



by drought, and hence should be given the culture that 

 best promotes soil moisture, as abundant surface tillage 

 and liberal manuring (231). 



125. Life of a leaf. — Leaves are usually short-lived 

 because they become clogged with those mineral matters 

 taken up with the soil water which are not used by the 

 plant (63) and which do not pass off in transpiration (74). 

 In most annual plants (337), the older leaves become use- 

 less from this clogging and die before the stem is fully 

 developed, and in most perennials the leaves endure but 

 a single season. In the so-called evergreen plants, in 

 which the leaves are usually very thick and are often well 

 protected against evaporation by a very strongly developed 

 cuticle (64), the leaves rarely live more than a few years. 



126. The manurial value of leaves that mature on 

 the plant is usually small, since the more valuable fer- 

 tilizing materials they contain pass into the stem before 

 the leaves ripen (170). The mineral matters contained 

 in largest quantity by leaves are those that are not used 

 by the plant, but have been deposited with them during 

 transpiration (125). 



THE BUDS 



127. The buds. — Each tip of the stem (66) is in most 

 plants protected with a covering of rudimentary leaves 

 or leaf-scales, and the tip with its leafy or scaly covering 

 constitutes a bud. A bud forming the apex of a shoot 

 is called a terminal bud; one at the junction of a leaf 

 with the stem (axil) is called an axillary or lateral bud 

 (Fig. 37). 



Each bud generally includes one terminal and several 

 axillary growing points. Aside from these, which in the 

 stem exist only in the bud, a bud is simply a part of the 



