68 



GROWTH AND WORK OF PLANTS 



farther than this slender terminal portion. The sumac is further 

 interesting because of the hairy condition of the shoots; the 

 absence of bud scales, their function being performed by a dense 

 woolly covering; by the resinous or gummy ex- 

 udation where bruised or cut, and by the large 

 size of the medulla or pith. The leaf scars are 

 peculiar in that they nearly surround the buds, 

 but are open above and nearly heart shaped. 



113. Shoots of the willow. The shoots of 

 the willow possess an axillary terminal bud and 

 the dead terminal portion of the shoot is crowded 

 to one side. The growth of the willow shoot 

 therefore is indefinite. The leaf scar is semi- 

 lunar in form and there are three bundle scars, 

 one below and one at each end. There is but 

 a single brown scale on the bud, and it fits over 

 the bud like a cap or hood. On removing it the 

 character and condition of the bud within is seen. 

 It is green and the young leaves are hairy. In 

 the spring when growth begins the bark is easily 

 removed from willow shoots. The willow is a 

 splendid example of the formation of adventi- 

 tious shoots and roots. They are developed in 

 great numbers when a shoot is placed in water 

 or in moist ground, and the willow is therefore 

 very easily propagated from cuttings. 



113. Leaf arrangement or phyllotaxy. 

 The arrangement of leaves on the shoot follows 

 in general certain well-known systems. While 

 there are certain variations and departures from 

 the normal, on the individuals of a given species 



Fig> 62 ' 



base of termini mr- the arrangement is the same. The arrangement 



tion and dead leaf. ^ ^ studied Qn leafy s h OO tS, Or On winter 



shoots, since the leaf scars and axillary buds mark the position 

 of the leaves. Leaves are either opposite or alternate. The 

 pairs of opposite leaves usually alternate at right angles with 



