6 ANGULAR DIVERGENCE [CH. 



Pear, Apple, Currant, Ficus religiosa, and very many other 

 dicotyledonous plants, the phyllotaxy is expressed by f ; 

 the upper number denoting that our line passes spirally 

 twice round the stem, and encounters five insertions before 

 again coming to the leaf vertically above our starting 

 point. 



In the same way we arrive at the fact that the phyllo- 

 taxy of the Radish, the Cabbage, Flax, Holly, Aconite, and 

 Plantain, with some others, is octostichous, , and higher 

 numbers such as f^, 8 T , f, &c, are to be met with 

 occasionally. See also Vol. I. p. 32. 



For certain purposes these facts are sometimes ex- 

 pressed in diagrammatic form by projecting the above 

 spirals on a plane, and marking all the leaf-insertions on 

 the line : the fraction of a circle described in passing from 

 any one insertion to the next is then spoken of as the 

 angular divergence of the leaves. 



In all these cases, and in those that follow, however, it 

 must not be overlooked that many plants exhibit more than 

 one kind of phyllotaxy, according as we select vertical or 

 horizontal branches, and it is particularly common to find 

 the phyllotaxy of the young seedling or of the basal part 

 of a shoot quite different from that of the older plant 

 or its parts ; this is still more emphatically the case when 

 we take also into account the leaves which have become 

 adapted to special purposes. 



At present, however, we are concerned only with the 

 ordinary typical foliage-leaves. The various cases so far 

 considered may all be regarded as coming under one 

 general heading, and their phyllotaxy may then be termed 

 alternate, or scattered : strictly speaking the former of 

 these two terms refers to the distichous arrangement (^), 

 but it is so commonly employed for all the above cases, that 

 it seems unnecessary to limit it further. 



