140 THE SCIENCE OF LIFE. 



a terminal bud. Buds are also developed in the axils of 

 the leaves, and some of them grow into branches, which 

 repeat the characters of the stem ; but others, when the 

 plant is fully developed, grow into stalks which support 

 the flowers. 



In Chap. IX, Sec. II, will be found a general descrip- 

 tion of the flower, and in Chap. IV, Sec. n, an account 

 of the tissues forming the leaf. The arrangement of 

 leaves and branches is also a subject of biological in- 

 terest. The mode in which branches come off from 

 the nodes gives rise to various forms of trees, such as 

 pyramidal, spreading, or weeping. In the Italian Pop- 

 lar and Cypress the branches are erect, forming acute 

 angles with the upper part of the stem ; in the Oak and 

 Cedar they are spreading ; while in the Weeping Wil- 

 low and Birch they are pendulous from their flexibil- 

 ity. Leaves also are placed in a fixed order for every 

 species of plant, and this order may be expressed by an 

 arithmetical formula. The arrangement of the leaves 

 on the axis is called phy Hot axis, (phyllon, a leaf; taxis, 

 order.) Each node of the axis may give rise to a leaf, 

 but sometimes several nodes are approximated nearly 

 together, and then several leaves may be produced at 

 the same height on the stem. When two leaves are at 

 the same level, one on each side of the stem, they art- 

 called opposite ; when a circle of leaves is thus produced 

 it is called a verticil, or whorl. When a single leaf is 

 produced at a node, and the nodes are separated, the 

 leaves are alternate. The relative position of alternate 

 leaves varies in different plants, but is tolerably uniform 

 in each species. In a regularly-formed branch covered 



