BUDS 127 



important purposes to be served ; the leaves must be 

 stowed as closely as possible in the bud, and upon begin- 

 ning to open they must be protected from too great heat 

 and dryness until they have reached a certain degree of 

 firmness. It may be inferred from Fig. 87, I, that it is 

 common for very young leaves to stand vertically. This 

 protects them considerably from the scorching effect of the 

 sun at the hottest part of the day. Many young leaves, 

 as, for instance, those of the silver-leafed poplar, the pear, 

 the beech, and the mountain ash, are sheltered and pro- 



FIG. 87, II. Development of an Oxalis Leaf. 



A, full-grown leaf ; B, rudimentary leaf, the leaflets not yet evident ; C, more 

 advanced stage, the leaflets appearing ; D, a still more advanced stage ; 

 B, C, and Z>, considerably magnified. 



tected from the attacks of small insects by a coating of 

 wool or down, which they afterwards lose. Those of the 

 tulip tree are enclosed for a little time in thin pouches, 

 which serve as bud-scales, and thus entirely shielded from 

 direct contact with the outside air (see Sect. 117). 



138. Dormant Buds. Generally some of the buds on a 

 branch remain undeveloped in the spring, when the other 

 buds are beginning to grow, and this inactive condition 

 may last for many seasons. Finally the bud may die, or 

 some injury to the tree may destroy so many other buds 

 as to leave the dormant ones an extra supply of food, and 



