386 



Gibb : The Study of a Fircone 





In studying the general arrangement of leaves upon the 

 stems of plants, botanists have found that, although the fact is 

 so often masked by circumstances that it is by no means patent 

 to ordinary observation, the fundamental principle of leaf 

 arrangement is a spiral form, in which if we count the number 

 of coils made by the spiral round the stem, and the number 

 of leaves it passes through in each complete turn, a series of 

 numbers is shewn, of which any two contiguous ones when 



added together will make 



the next in the series. These 



are the so-called phyllo- 



taxian numbers, usually 



written with No. of coils 



as numerators and No. of 



leaves as denominators, 



fhnQ • 1 2 3 _5_ _8_ 2,X\(\ 



SO on. 



In fig. I representing six 



leaves growing up a stem 



(taken from Piitosporhim 



undtdatum) the coil, repre- 

 sented by the dotted line, 



passes through three leaves 



in its first complete turn, 



and through two more in its 



second turn, thus exhibiting 

 the first two numbers of the above series : — 

 I", f . The sixth leaf stands directly above the 

 first, shewing that for this particular plant the 

 order of the leaf arrangement is completed in 

 five leaves. However long the shoot might 

 be, the positions of those five leaves round the 

 stem would just be repeated over and over 

 again, and as the sixth leaf stood over the 

 first, so would the eleventh, sixteenth, twenty- 

 first, and every fifth leaf onward, the coil passing through three 

 and two leaves alternately in never-ceasing monotony of 

 rhythm. The rose has a similar series of. five leaves, and 

 sings to the same simple song of coil and leaf, 3 ,2 ; 3, 2 ; 3, 2. 

 A slightly more complicated arrangement is shewn in fig. 2, 

 from the common holly, whose prickly leaves have been cut off 

 in order to shew clearly the arrangement of their growth on 



Naturalist, 



Fig. I. 



From Pitiospoi'iiim 

 iindiilatum. 



Fig. 2. 



From Common 

 Hollv. 



