230 



BOTANY OF THE LIVING PLANT 



but it is best not to overload them. As examples the following 

 formulae for common flowers may be given : 



Lily, P 3 + 3 , A 3 + 3 , G(3). (Compare Fig. 178.) 

 Buttercup, S 6( P 6 , A oo , G %_. 

 Myrrhis,S 6 ,P 6 ,A 6 ,G(2y. 

 Primrose, (SJ, (P^A^, G (5). 



[For details which will explain these formulae see Appendix A.] 



FACTORS LEADING TO DIFFERENCES OF FLORAL CONSTRUCTION. 



The leading factors will now be stated and discussed upon which 

 the differences of floral construction chiefly depend. They are these : 



(i) The arrangement of the parts upon the receptacle may be either 

 spiral, as in Adonis (Fig. 179) ; or cyclic, as in Ornithogalum (Fig. 178) ; 



FIG. 179. 



Floral diagram of A donis 

 (From Strasburger.) 



FIG. 180. 



Floral diagram of Helleborus. (After 

 Church.) 



or an intermediate condition (hemicyclic) may be found between them, 

 as in some of the Buttercup Family (Fig. 180). The cyclic type is 

 however prevalent, especially in highly organised flowers. Since the 

 spiral is characteristic of many primitive flowers and these graduate 

 into cyclic types, the facts suggest that the cyclic state may often 

 have been derivative in Descent. The parts of successive whorls or 

 even in spirals also, alternate as a normal rule. This allows of their 

 close packing in the bud. They are formed in acropetal succession. 

 Occasionally it is otherwise, but the most prominent exceptions occur 

 where an organ is reduced, as in the calyx of the Compositae. 



