PHYLLOTAXY. 



127 



First separate the specimens having opposite and verti- 

 cillate leaves from those with alternate leaves. 



Observe that the successive pairs of leaves in opposite- 

 leaved plants are placed at right angles to each other, 



FIG. 393. 



each leaf of the upper pair being placed over a space left 

 by the lower pair. They are hence called decussate leaves. 

 In the same way the whorls of leaves in verticillate-leaved 

 stems are so placed that they alternate with each other. 



Observe the arrangement of leaves in the stems of 

 grasses, and in stems with equitant leaves. 



Put by themselves all the stems in which the leaves 

 are neither decussate nor whorled. 



Examine them, one after the other, thus : Take a 



