THE LIVING PLANT 27 



Before stored food can be used by the plant, it must be 

 changed again into soluble forms. By action of certain 

 substances known as enzymes or ferments, plants are able 

 to change starches to sugars and sugars to starches readily. 



42. Growth of stems. How stems grow in diameter has 

 already been explained. Stems elongate from growing points 

 or buds. An examination will show that there are nodes or 

 joints at the points from which the leaves grow out. The parts 

 between the nodes are designated internodes. The inter- 

 nodes do not elongate after the first growing season is past. 



43. Buds. Several kinds of buds are formed from certain 

 tissues of the outer portion of stems. Buds may be classified 

 according to function as leaf, flower, and mixed buds. A 

 leaf -bud consists of a very short axis having internodes so 

 short that the nodes are packed closely together. At these 

 nodes are very small undeveloped leaves. The bud may be 

 covered with protective scales, as in most perennials (plants 

 which live for more than two years), or they may not have 

 protective scales and are then said to be naked, as in many 

 herbaceous plants. A leaf-bud is really a potential stem. It 

 elongates into a stem and its leaves develop into the foliage. 

 A flower-bud develops into flowers which under favorable 

 conditions set fruit. The number of flowers differs in the 

 various buds; for example, in the cherry the number is from 

 three to five, in the plum two or three are common. Mixed 

 buds contain both flowers and leaves, as in the apple. 



Buds may be active, dormant, or adventitious. Active 

 buds are those that grow under normal conditions. Dormant 

 buds do not grow to any extent, but possess the power of 

 growth should favorable conditions arise. As a rule, buds near 

 the tip of twigs are more active than those at the base, many 

 of which are dormant during the growing season. Of course, 

 all buds are dormant in the winter in cold climates. Adventi- 

 tious buds are not visible but arise from unusual conditions, 

 such as injury. 



