28 



LEAF ARRANGEMENT 



or interfering with one another. Furthermore the arrangement 

 is such as to occupy practically all the space about the stem that 



m, 



FIG. 13. FIG. 14. 



FIG. 13. Branch of /oryytf/wa, leaves decussate, in four rows. 



FIG. 14. Branch of poplar with leaves spirally arranged in five rows. 



receives light. This becomes very noticeable if we look directly 

 down upon a shoot or better if we stand under a tree and look 

 up into the branches. It will be seen that very little direct sun- 

 light finds its way through the branch, so nicely are the leaves 

 adjusted to each other. Some plants like the hickories, catalpa, 

 etc., occupy all the available space with a few large leaves at the 

 tips of the branches. In other cases, as in the willows, some 

 lilies, etc., the same result is accomplished by many small leaves 

 that can be arranged along the stem for considerable distances 

 without shading. The nicety of leaf arrangements is especially 

 noticeable in many horizontal and creeping stems. In such cases 

 the leaves can only be exposed on the sides of the stem and con- 

 sequently the stem may become twisted or more usually the 



