408 RELATION TO ENVIRONMENT. 



leaf just below. In some stems, according to the leaf arrange- 

 ment (or phyllotaxy), one would pass several times around in 

 ascending the stem before a leaf would be found directly above 

 another, which would be such a distance below that it would not 

 be shaded to an appreciable extent. Interesting observations 

 can be made on different plants to work out the relation of dis- 

 tance of leaves on the stem to length of the upper and lower 



Fig. 446. 



Palm showing radiate arrangement of leaves and the petiole of the leaf func- 

 tions as stem in lifting leaf to the light. 



leaves; the number of vertical rows on the stem compared to 

 the width of the leaves; and the relation of these facts to the 

 problem of light supply. Related to the spiral pattern is that of 

 erect stems with opposite leaves. Here each pair is set at right 

 angles to the direction of the pair above or below. 



781. Radiate pattern. This pattern is present in many grasses 

 and related plants with narrow leaves and short stems. The 

 leaves are often very crowded at the base, but by radiating in 

 all directions from the horizontal to the vertical, abundant ex- 



