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TEXTBOOK OF BOTANY 



ing ( Fig. 88 ) . Although these types of branching are readily distinguish- 

 able, all gradations among them occur. 



The form of a plant is thus seen to depend on the relative development 

 of terminal and lateral buds. As indicated above, advantage is taken of 

 this knowledge by florists, gardeners, and orchardists. Various orna- 

 mental effects in lawn trees and shrubs may be obtained by removing the 

 terminal buds that inhibit the growth of the lateral buds. Fruit trees and 

 grape vines are "pruned" to regulate the shape of crowns as well as the 

 number and spacing of the branches. 



Fruit spurs. It was indicated earlier that the age of a twig could be 

 determined by counting the number of scars left in successive years by 

 the terminal buds. The distance between two such scars may be indica- 

 tive of the favorable or unfavorable conditions under which the plant 

 grew in a particular year, or it may be indicative of local internal 

 conditions. 



On fruit trees such as apple and pear, the flower buds often occur at 

 the ends of short stems known as "spurs." When the terminal bud is a 



Fig. 89. Fruit spur of apple. Fruits were borne every other year, as indicated 

 by the large scars on the annual stem segments formed during odd-numbered 

 years. Courtesy of J. H. Gourley. 



flower bud, subsequent elongation of the spur is dependent on a lateral 

 bud. Frequently the spurs bear flowers only in alternate years, and the 

 fruit scars are found only on alternate annual segments of the spur 

 (Fig. 89). The spurs usually continue to bear flowers and fruits for 

 many years and grow much more slowly than the vegetative branches. 

 Successive development of lateral buds results in a crooked spur. The 

 interval between successive terminal bud scale scars is exceedingly 

 short during the years that fruits are borne. 



Saint John's shoots. Some trees, such as elms, hackberry, and certain 

 oaks, have two periods of stem elongation each growing season: one in 

 early spring and another in early summer. The twigs of citrus trees in 



