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LEARNING TO NAME PLANTS 



23 



Fig. 18. Diagram of leaf arrangement on stems, as seen from above and from the 

 side. A, oppositely arranged leaves; B-D, alternately arranged leaves. B, the one- 

 half, or two-ranked, arrangement; C, the one-third, or three-ranked, arrangement; 

 D, the two-fifths, or five-ranked, arrangement. 



that is, the spiral passes through 3 nodes before completing a cycle and 

 the fourth leaf -base is directly ov er the first — thev are said to have the 

 1/3 alternate arrangement. These leaves occur in three ranks on the 

 stem. This arrangement is best seen in the sedges. 



Many trees have a more complicated leaf alignment. A spiral drawn 

 around the stem from one bud to another directly below it passes through 

 5 nodes and twice around the stem; the sixth bud is directly below the 

 first bud. This arrangement is called the 2/5 alternate type. Still other 

 leaf and scale arrangements may be found, such as 3/8, 5/13, 8/21. The 



