Ch. IV, 



ARRANGEMENTS OF LEAVES 



141 



forming two vertical ranks and bringing the tliircl leaf over 



the first (Fig. 95), as well manifest in Corn and other 



Grasses. In other cases, the leaves stand 



one-third of the circumference apart, 



forming an ob\ious spiral, bringing the 



leaves into three vertical ranks with a 



fom-tli over a first (Fig. 96), as in Sedges, 



which, correlatively, have triangular 



stems. The next of the arrangements 



actually found is that where the leaves 



stand two-fiiths of the circumference 



apart (Fig. 97), in which case the spiral 



must turn t'ndce around the stem before 



a leaf, the sixth, is reached over the first, 

 five vertical ranks 

 resulting. This is 

 the commonest of 

 the alternate ar- 

 rangements. It is 

 very clear in the 

 Apple, and in many 

 common plants, 



though at times, in long stems, its regu- 

 larity is disturbed by some twist of the 

 stem. It underlies the prevalence of the 

 number five in the plan of most flowers, as 

 the one-third and one-half arrangements 

 undcrhe the numbers three and four in 

 others. The next arrangement is that 

 of three-eighths (Fig. 98'. found in the 

 Holly. The next is that of five-thir- 

 teenths (Fig. 99\ found in the House- 

 leek, which forms the famihar rosettes, 

 while in Pine cones and other such struc- 

 tures, arrangements of eight twenty-firsts, and even thirteen 



thirtv-fourths and twenty-one fifty-fifths have been deter- 



FiG. GO. — The alter- 

 nate. ^ spiral, arrange- 

 ment. 



Fig. 97. — The alter- 

 nate, f spiral, arrange- 

 ment. 



