LEAVES— FORM AND POSITION 



83 



stands east and west. See the box-elder shoot, on the 

 left in Fig. 1 10. One pair does not shade the pair beneath. 

 The leaves are in four vertical ranks. 



There are several kinds of alternate arrangement. In the 

 elm shoot, in Fig. 1 10, the third bud is vertically above the 

 first. This is true no 

 matter which bud is taken 

 as the starting point. 

 Draw a thread around 

 the stem until the two 

 buds are joined. Set a 

 pin at each bud. Ob- 

 serve that two buds are 

 passed (not counting the 

 last) and that the thread 

 makes one circuit of the 

 stem. Representing the 

 number of buds by a de- 

 nominator, and the num- 

 ber of circuits by a 

 numerator, we have the 

 fraction J, which expresses 

 the part of the circle that lies between any two buds. 

 That is, the buds are one half of 360 degrees apart, or 

 180 degrees. Looking endwise at the stem, the leaves 

 are seen to be 2-ranked. Note that in the apple shoot 

 (Fig. 1 10, right) the thread makes two circuits and five 

 buds are passed : two-fifths represents the divergence 

 between the buds. The leaves are S-ranked. 



Every plant has its own arrangement of leaves. For 

 opposite leaves, see maple, box elder, ash, lilac, honey- 

 suckle, mint, fuchsia. For 2-ranked arrangement, see 

 all grasses, Indian corn, basswood, elm. For 3-ranked 



Fig. iio. ■ 



- Phyllotaxy of Box Elder, 

 Elm, Apple. 



