330 A TEXTBOOK OF BOTANY [Ch. VI, 10 



Typically, and usually, the floral whorls alternate, as in 

 the case of leaves on the stem (page 140). Most of the 

 exceptions are only apparent, as in the Lily family (Fig. 226), 

 where a whorl of six stamens seems to stand opposite a 

 whorl of six petals or sepals (e.g. Lily of the Valley) ; but 

 in reality whorls of sepals and petals, here alike, and two 

 whorls of stamens regularly alternate. In case of the 

 Primrose, where five stamens stand opposite five petals 

 (Fig. 227), it is likely that another set of five stamens, which 

 would make the alternation perfect, has vanished in the 

 course of evolution. Indeed, two whorls of stamens are 

 more frequent, and perhaps more " typical" than one. 

 The usual lesser number of carpels, of course, destroys the 

 alternation in their case. 



Typically the sepals, petals, stamens, and carpels all 

 stand separate and distinct upon the receptacle, precisely 

 as do leaves on the stem ; but sometimes each whorl forms a 

 single structure. Thus the calyx, as earlier noted (page 270), 

 is often one structure at base, and even to near its top, while 

 sometimes it forms a tube with only small teeth on its free 

 margin, e.g. Phlox. It was formerly supposed that such a 

 calyx is formed by a union of the lower parts of the sepals, 

 the tips alone remaining free, on which account it was called 

 gamosepalous (united sepals) in distinction from polysep- 

 alous applied to the separate condition. This view, how- 

 ever, finds no support in the development of the indi- 

 vidual flower, where no such union of parts takes place; 

 for, in fact, the sepals originate and grow separately for a 

 time, and then are lifted by the growth of a continuous ring 

 of leaf-like tissue, which gradually elongates to the tubular 

 part of the calyx. It is possible that in course of their 

 evolution the sepals have become united, as the older view 

 held; but it is equally possible, and much more in accord 

 with the method of their present development, that only the 

 free tips represent the original separate leaves, while the 

 tubular part is a new development, just as we know the 



