BUDS AND LEAF ARRANGEMENT. 5 I 



dicotyledons, e.g., willow, oak, rose, apple, and cherry, display 

 five-ranked or quincuncial (§) phyllotaxis (fig. 9). Here there 

 are five orthostichies and five leaves in the cycle, which makes 

 two turns round the stem. An eight-ranked (f) case may be 

 seen in the holly, while the other divergences chiefly occur in 

 cases where the leaves are much crowded. The house-leek, for 

 example, presents the thirteen-ranked ( T 5 ^) arrangement. It 

 frequently happens that irregularities are Drought about from 

 twisting of the stem and other causes. In the elm and beech, 

 for instance, the two ranks of leaves are not exactly opposite each 

 other, but are nearer together on the under than on the upper 

 side of the branch. Here also we get a bilateral arrangement, 

 i.e., the leaves are all approximately in the same plane ; hence 

 it becomes possible to distinguish between upper and lower sur- 

 faces in the branch. This also is caused by displacement of 

 parts. 



We now come to a consideration of the kinds of leaf. These 

 are generally taken to be four in number : — 



1. Foliage (euphyllary) leaves. 



2. Scale (cataphyllary) leaves. 



3. Bracts (hypsophyllary) leaves. 



4. Floral leaves. 



These will be described in the following chapter. 



