OEGANS OF NUTRITION. 



139 



apple {fig. 266), and in the fruit of Coniferous Plants {fig. 267), 

 the spiral arrangement is at once evident. 



By placing the fractions representing the angular divergence 

 in the different varieties of Phyllotaxy side by side in a line, 

 thus :-^, I, f, f, ^, ^, If, e, &c.; \, I I, A, ,^, ^, &c., we see 

 at once that a certain relation exists between them ; for the nu- 

 merator of each fraction is composed of the sum of the mmie- 

 rators, and the denominator of the sum of the denominators of 

 the two preceding fractions ; also that the numerator of each 

 fraction is the denominator of the next but one preceding. By 

 applying this simple law t-herefore we may continue the series of 

 fractions representing the angular divergence, &c., thus : — 1|, 

 —i, T^^3, &c. It should be mentioned with respect to the laws of 

 Phyllotaxy, that they are frequently interfered with by accidental 

 causes which produce corresponding interruptions of growth, so 



Fig. 266. 



Fig. 267. 



Fig. 266. Pine-apple fruit 

 (Sorosis), surmounted 

 by a crown of empty 



bracts. Fig. 267. Cone 



or fruit of the Scotch 

 Fir. 



that it is then difficult, or altogether impossible, to discover the 

 regular condition. 



All the above varieties of Phyllotaxis in which the angular 

 divergence is such that by it we may divide the circumference 

 .into an exact number of equal parts, so that the leaves com- 

 pleting the cycles must be necessarily directly over those com- 

 mencing them, are called rectiserial, to distinguish them from 

 those in which the divergence is such that the circumference 

 cannot be divided by it into an exact number of equal parts, 

 and thus no leaf can be placed precisely in a straight line over 



