112 



Science of Plant Life 



year's growth is marked 

 by a whorl of branches, 

 and the age of a tree may 

 readily be estimated by 

 counting the nmnber of 

 whorls on the stem. Since 

 the oldest branches are 

 nearest the ground they 

 are the longest, and the 

 tree becomes cone-shaped 

 as it grows. 



The terminal buds of the 

 ehn tree seldom survive the 

 winter. The lateral buds 

 develop, and the main stem 

 divides and subdivides im- 

 til it is lost in the crown 

 of the trees. This gradual dissolving of the trunk into a 

 spray of terminal branchlets suggested the name deliquescent 

 (Latin: deliquescens, dissolving) for this type of stem. We 

 see, therefore, that the excurrent type of stem depends on 

 the continual development of terminal buds, while the deh- 

 quescent type depends on the growth of lateral buds. Con- 

 sequently we may modify the forms of plants in cultivation 

 by trimming them and so forcing the growth of certain buds. 

 Lawn trees and shrubs are grown either for shade or for 

 ornamental effects. We secure shade by trimming off the 

 terminal buds and so causing many of the lateral buds to 

 develop into branches and thus form a denser crown. Orna- 

 mental effects are secured by trimming plants so that they 

 will be in artistic harmony with their surroundings. 



Fig. 66. A hackberry in Illinois. The de- 

 velopment of the lateral buds results in the 

 formation of a deliquescent stem. 



