PHYLLOTAXY, OR LEAF ARRANGEMENT 



43 



senting the two kinds of arrangement as viewed from 

 above. Notice that if we join the leaves in the opposite 

 arrangement by dotted lines we shall get a series of circles 

 (Fig. 75), while the alternate arrangement will give a spiral 

 (Fig. 76). 



These two kinds of insertion, the alternate and opposite, 

 represent the fundamental forms of leaf disposition. There 

 may be varieties of each, but no matter what minor differ- 

 ences exist, all may be referred to one of these 

 two modes. 



51. Whorled and Fascicled 

 Leaves. Where more than 

 two leaves occur at a node 

 they constitute a whorl, or ver- 

 ticel, as in the trillium and 

 common cleavers (Gallium}. 

 There is no limit to the num- 

 ber of leaves that may be in a 

 whorl except the space around 

 the stem to accommodate them. 

 A 'fascicle, or cluster, of 

 which the pine and 

 larch furnish exam- 

 ples, is composed of alternate leaves with very 

 short internodes, which bring the leaves so close 

 together as to give them the 

 appearance of a whorl. 



52. Varieties of Alternate 

 Arrangement. The kind of 

 alternate arrangement just 

 described is called the two- 

 ranked, because it distributes 

 the leaves in two rows on 

 opposite sides of the stem ; 

 in other words, each is just halfway round from the one 

 next above or below it. Other common forms of the alter- 



77 78 



77-78. Whorls and fascicles : 77, 

 whorled leaves of Indian cucumber; 

 78, fascicled leaves of pine. 



79~8o. Three-ranked arrange 

 ment: 79, vertical diagram; 80, hori 

 zontal diagram. 



