ADVENTITIOUS BUDS 87 



in thin pouches, which serve as bud scales, and are thus entirely 

 shielded from direct contact with the outside air. 



101. 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 this, with other causes, may 

 force them to develop and to grow into branches. 



Sometimes the tree altogether fails to produce buds at places 

 where they would regularly occur. In the lilac the terminal 

 bud usually fails to appear, and the result is constant forking 

 of the branches. 



102. Adventitious buds. Buds which occur in irregular places, 

 that is, not terminal nor in or near the axils of leaves, are called 

 adventitious buds; 



they may spring from 

 the roots, as in the 

 silver-leafed poplar, or 

 from the sides of the 



trunk, as in our Amer- 



-, T FIG. 88. Budding leaf of Bryophyllum 



ican elm. In many 



trees, for instance willows and maples, they are sure to appear 

 after the trees have been cut back. Willows are thus cut back, 

 or pollarded, in order to cause them to produce a large crop of 

 slender twigs suitable for basket making. 



Leaves rarely produce buds, but a few kinds do so when they 

 are injured. Those of the Bryopliyllum (Fig. 88), a plant allied 

 to the garden live-forever, when they are removed from the plant 

 while they are still green and fresh, almost always send out 

 buds from the margin. These do not appear at random, but 

 are borne at the notches in the leaf margin and are accompa- 

 nied almost from the first by minute roots. This plant seems to 

 rely largely upon leaf budding to reproduce itself, for in a cool 

 climate it rarely flowers or seeds. 



