14 THE STRUCTURE OF FLOWERS. 



in the leaves, as in GaryophyllecB and Labiates. This may 

 be due either to an abrupt change from opposite leaves or 

 bracts to a spiral one in the flower, or by a reversion 

 from an alternate to an opposite position of the leaves,' the 

 floral organs retaining the arrangements due to their spiral 

 origin. 



The symmetry is based on Calyx, Corolla, and in many 

 cases the Androecinm also ; but the carpels are not generally 

 regarded, for it does not usually extend to the gyncecium, 

 though it is very frequently retained in the andrcecinm, 

 which is often some multiple of that of the perianth 

 whorls. 



In presenting the reader with what may be regarded as 

 ostensible grounds for the interpretation proposed, attention 

 will be first directed to the more obvious correlations be- 

 tween floral symmetry and leaf arrangements, as appear 

 from certain numerical proportions ; and, in the next chapter, 

 to significant facts observable in the symmetry of particular 

 plants. 



Commencing with genera possessing alternate leaves and 

 a quinary floral type, the prominent fact becomes at once 

 apparent that this correlation far exceeds in nnmerical 

 proportion any other. Thus, of above eighty Dicotyledo- 

 nous orders* examined in all, no less than 1285 genera 

 have quinary flowers associated with alternate leaves, and 

 this is exactly what (5ne wonld expect according to the 

 theory advanced that 5-merons whorls are cycles of the 



% type- 

 As a corroboration is the fact that such whorls often 

 have their parts arranged quincuncially in aestivation (Fig. 

 3, a) ; and when they are not so they can be referred to 



* I conanlted the first volume of the Qenera Plantarum for this 

 purpose, which embraces the Thalamifiorce and Calyciflor(e. 



