56 SPIRAL ARRANGEMENT [CH. 



through that of the next one, on through the insertions 

 of the six petals, the numerous stamens, and the spirally 

 arranged carpels, right to the apex of the shoot. The 

 terminal flower of Berberis is also spiral in the arrange- 

 ments of its parts, though the turns 

 are so close that it appears whorled 

 (Fig. 17). 



Even here, however, we notice 

 the initiation of one of the most 

 important phenomena in the evolu- 

 tion of the flower ; namely, that the 

 Fig. 17. Terminal flower insertions of the sepals and petals 

 of a Barberry, seen are go near ly a fc the same level that 

 the spiral nature of the line joining 



them is only detected by close observation. In most 

 flowers, we shall find that the organs of like kind are 

 inserted at the same level, in cycles or whorls around 

 the axis, due to the shortening or suppression of the 

 internodes : these cases are exactly comparable to the cases 

 where foliage-leaves come to be inserted in whorls instead 

 of in spirals, and obviously the whole subject of arrange- 

 ment of these floral leaves is one of Phyllotaxy. 



More or less completely spiral arrangements of the 

 various floral organs are met with in the flowers (cones) 

 of Pines, Firs, &c., and in a few groups of exotic plants, 

 Calycanthacece. 



It is commoner even in ordinary flowers of such 

 groups as those referred to, however, to find that the 

 sepals and petals are in whorls, and show no spiral 

 arrangement, whereas the stamens and carpels are dis- 

 tinctly inserted along an ascending spiral. 



Commoner by far, however, is the arrangement of all 

 the organs in cycles or whorls, and the flower ceases to 

 show any traces of its spiral structure. This is due, in 



