100 THE STRUCTURE AND WORK OF THE STEM 



weather, only to thaw out again without injury to the plant. Sudden 

 changes, however, do much harm. Some buds do not open during mild 

 winter weather when temperature 

 conditions are seemingly favorable ; 

 a definite length of growth seems 

 in that case to be necessary. Dur- 

 ing warm weather plants give rise 

 to buds "\\hich are devoid of pro- 

 tective scale leaves. Such is also 

 noticed in tropical forms, which are 

 not called upon to meet rigorous 

 climatic conditions. 



Position of the Bud on the 

 Stem. — The growth of the stem 

 from the bud can best be observed 

 in a ^-ery young seedling. If, for 

 example, we examine a pea seed- 

 ling, it will be seen that the plumule 

 or epicotyl is the first bud of the 

 plant. It produces the first stem 



and leaves. Buds come out 

 at the ends of branches 

 (terminal) and at the sides 

 {lateral}. 



Deliquescent Tree. — 

 The position of the most 

 active buds determines the 

 form of the future tree. If 

 you examine a ■winter branch 

 of the apple, elm, or oak 

 tree, you will find that the 

 lateral buds have developed 

 more strongly and more rapidly than the terminal bud. Thus the tree has 

 come to assume during its growth a rounded shape due to the rather 

 more rapid development of the lateral buds. Such a tree, having a 

 rather stout, short trunk, with many low, spreading, lateral branches, 

 is said to be deliquescent. 



A larch, an excurrent tree (at rightj and an elm, 

 a deliquescent tree (at left) . Photographed by 

 W. C. Barbour. 



