26 BOTANY OF CROP PLANTS 



ence really exists can be well shown by removing branches or 

 buds and growing them into independent plants. If we do 

 this we will find that the individuals from the separate buds 

 may vary in such respects as habit of growth, manner of 

 branching, nature of foHage, form, color, texture and yield 

 of fruits. 



Nearly all our fruits are multiplied by bud propagation 

 (asexual parts) and not by seed (sexual parts) ; and many of 

 the varieties of fruits now in cultivation are in reality bud 

 varieties or " sports." A certain branch on a tree is observed 

 to differ from the rest in some marked respect; and this 

 branch is taken off and propagated as a new variety. 



General Characteristics of Steins. — ^Let us now examine a 

 winter twig of the Cottonwood, for example, that is several 

 years old, such as pictured in Fig. lo. At the tip is a large 

 terminal bud. If it is broken open, young overlapping leaves 

 are found within. It develops into a leafy branch. The 

 growth in length of the shoot results from the lengthening 

 of the internodes in the bud. Along the side of the stem are 

 lateral buds at regular intervals. These may be leaf buds or 

 flower buds, as can be positively determined by breaking 

 them open. Below each bud there is a half-moon-shaped leaf 

 scar. Hence we see that leaf arrangement is also bud ar- 

 rangement. By examining the leaf scar with a hand lens 

 one sees several small bundle scars on the surface. Bundle 

 scars are left by the vascular bundles that pass from the 

 woody stem into the petiole (stem) of the leaf. Inflorescence 

 scars are large circular or oval scars left by the falling off 

 of flower clusters. A leaf scar is observed beneath each 

 inflorescence scar. The twig growth of each year is clearly 

 distinguished by a ring of scars. When the closely arranged 

 bud scales of a terminal bud fall off in the spring they leave 

 a number of scars so close together as to make a ring. Hence 



