ISO DESCRIPTIVE BOTANY. PART I. 



an expression for the divergence, which is all that the 

 botanist requires. 



(126.) Irregularity of Divergence. Although the 

 appendages on one part of a plant, may be arranged 

 according to one law of divergence, it does not follow 

 that those of another kind, and on another part, possess 

 the same law ; and even the same kind of appendages 

 are not all subject to the same law : thus, a few cones 

 on the same fir tree often possess a different diverg- 

 ence from the rest, and even different parts of the 

 same cone are sometimes differently disposed. Many 

 of these anomalies originate in disturbing causes, which 

 it is not difficult to appreciate; such, for instance, as 

 some slight torsion of the axis, or the abortion of some of 

 the parts, &c. It is also common to find the generating 

 spiral turning to the right in some cones, and to the 

 left in others, upon the same tree. 



(127.) Examples of Divergences. From what has 

 been said, it will readily be seen, that the disposition of 

 foliaceous appendages may be conveniently and accu- 

 rately expressed, in terms of the divergence of the 

 scales on the generating spiral, unless they happen to 

 be so irregularly disposed as to lose all traces of a sym- 

 metrical arrangement. ' Thus, where the appendages 

 range in a line along one side of the axis, the divergence 

 is = ^ ; where they are ranged in two rows, on opposite 

 sides of the axis (distichous, fig. 139-), the 

 divergence = ^ ; when in three rows 

 (trifarious'), the divergence may be -^ or 

 -* : the latter, however, may be considered 

 the same as , turning round the axis in 

 an opposite direction. One of the most 

 common, the " quincunxial" arrangement, 

 where the appendages range in five ranks, 

 may be produced by four different diverg- 

 ences, represented on the circles in the an- 

 nexed figure (fig. 140.); but here also it will 

 be seen, that two of them are the same as 

 other two, only that the spirals turn 



