BOTANY OP THE LIVING PLANT 



t bility is common. It is styled meristic variation, and probably 

 on in producing it is the size of the apical cone, which, when 



large proportionally to the leaf-primordia, can accommodate a larger 

 Dumber of young leaves at the same level. Such variations are 



.union in the floral region, where cyclic arrangements prevail. 

 [Compare Floral Diagrams in Appendix A.) 



But in most Dicotyledons, and very generally in Monocotyledons, 

 the arrangement of the leaves is alternate] that is, they are seated 

 singly, each at a different level upon the axis. The arrangement is 



Fig. 135. 



A F. Ground-plans of buds of Sunflower of different ages : but these drawings are not 

 uniform in scale. See Text. (After Church.) 



often such that an ascending spiral line may be drawn round the 

 mature stem so as to thread together the bases of them all. Such 

 arrangements are therefore described as spiral. That the cyclic and 

 spiral modes of arrangement are not essentially distinct from one 

 another is shown by the fact that both may appear successively in 

 the same plant. For instance, in the Sunflower, the seedling starts 

 with paired cotyledons, followed by decussate leaves of the plumule 

 (Fig. 135, a), which arrangement may be maintained for a time (c) ; 

 but sooner or later irregularities appear (b), leading to an alternate 

 arrangement (dj, which becomes more complex in the upper vegetative 

 on (e), and culminates in the very complex structure of the 

 flowering head (Fig. 135, f). It will be unnecessarv for us to trace 



