PHYLLOTAXIS. 



41 



it is quite impossible to say which is the second leaf after having fixed 

 upon some one as the first. This is especially apparent in the case of 

 fir-cones, where the scales may be considered as the representatives of 

 leaves, and which, though crowded, are arranged in a strictly mathe- 

 matical order. 



If a cone of the Norway spruce fir be held vertically, the scales upon 

 it will be observed to run in a series of parallel spirals both to the left 

 hand and to the right. This is a result of their being crowded together, 

 as well as of their definite arrangement. It is the object of the observer 

 to detect and represent that order by some arithmetical symbol. This 



Fig. 2. 



may be done by attending closely to the following directions : — Obs. 1. 

 Fix upon any scale as No. 1, and mark the scales which lie in as nearly 

 a vertical line over it as possible, viz. numbered at 22, 43, 64, &c. Obs. 2. 

 Note the scales which are beloiv, nearest to, and overlap that scale (No. 

 22). Obs. 3. Run the eye along the two most elevated spirals, one to 

 the right hand, the other to the left ; and passing through the scales 

 which overlap the scale numbered 22.* Obs. 4. Count the number of 

 spirals (called secondary) which run round the cone parallel to these two 



* These spirals are shaded in the figure, so as to render them more conspicuous 

 viz. the spiral 1, 9, 17, 25, &c. to the right ; and 1. 14, 27, 40. &0. to the left. 

 I have said the most elevated spirals, because had I chosen the spiral passing through 

 the scales 1, 6, 11, 16, *c. the object of search would not have been obtained. 



