PHYLLOTAXY. 



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many leaves it passes on its way. If, in passing from the 

 first leaf to the one directly over it, the string makes but 

 one circuit around the stem, and the third leaf is over the 

 first, so that the cycle includes but two leaves, the fourth 

 leaf being over the second, and so on, you have an ar- 

 rangement like that seen in Fig. 393. The leaves in this 

 example are seen to form two rows along the side of the 

 stem, which are separated by half its diameter. 



This is the distichous, two-ranked, or \ arrangement. 



If, in passing from one leaf to another directly above 

 it, the string goes but once round the stem, and the 

 fourth leaf is over the first, giving a cycle of three leaves, 

 the arrangement is like that shown in Figs. 394 and 395. 

 There are three perpendicular 

 rows of leaves along the stem, 

 separated from each other by -J 

 its circumference. 



This is the tristichous, three- 

 ranked, or -J arrangement. 



Again, the string may pass 

 twice around the stem before it 

 reaches the leaf placed just over 

 the first, which, on counting, 

 proves to be the sixth (Fig. 

 397). There are five longitudi- 

 nal rows along the stem, sepa- 

 rated from each other by f its 

 circumference. 



This is the pentastichous, 

 quincuncial, or f arrangement. FlG - 395- FIG. 396. 



Observe that the numerator 



in the foregoing fractions gives the number of times the 

 string winds around the stem in completing a cycle, 

 while the denominator gives the number of leaves in the 

 cycle. 



This fraction is sometimes called the angle of diver- 



s 



