LEAVES FORM AND POSITION 



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 \ t 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 

 1 80 degrees. Looking endwise at the stem, the leaves 

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

 (Fig. no, right) the thread makes two circuits and five 

 buds are passed : two-fifths represents the divergence 

 between the buds. The leaves are 5-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. no. PHYLLOTAXY OF Box ELDER, 

 ELM, APPLE. 



