128 FOUNDATIONS OF BOTANY 
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. Inthe lilac the 
terminal bud usually fails to appear, and the result is con- 
stant forking of the branches. 
139. Adventitious Buds. — Buds which occur in irregu- © 
lar 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 American 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, as shown in Plate II, 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 bryophyllum, a plant allied 
to the garden live-for-ever, 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 accompanied almost from the first by minute roots. 
Pin up a bryophyllum leaf on the wall of the room or 
lay it on the surface of moist earth, and follow, day by day, 
the formation and development of the buds which it may 
produce. 
This plant seems to rely largely upon leaf-budding to 
reproduce itself, for in a moderately cool climate it rarely 
flowers or seeds, but drops its living leaves freely, and from 
each such leaf one or several new plants may be produced. 
