252 



MORPHOLOGY 



sion, the perianth consists of two sets of members, sepals and petals^ 

 which in general are foliar in nature, but differ more or less dis- 

 tinctly from the ordinary bracts or leaves of the plant (fig. 562). They 

 seem to have been derived, historically, from adjacent sporophylls and 

 adjacent bracts or foliage leaves ; in any event, they are intercalated as 

 distinct members between the bracts or foliage leaves on the one side, and 

 the sporophylls on the other. It is not clear what was the most primi- 

 tive condition of the flower among angiosperms; whether it began with 



FIG. 562. Section of flower of peony, showing sepals (&), petals (c), numerous stamens 

 (a), and apocarpous carpels (g). After STRASBURGER. 



a fully developed perianth, which in certain groups became reduced or 

 even suppressed ; or whether it began with no perianth, which first ap- 

 peared in very simple form and gradually became more highly developed 

 and complex. Both views have support. In any event, there are cer- 

 tain general facts and tendencies of the flower which are evident. 



Differentiation of perianth. A series of flowers can be arranged with 

 those having no perianth (naked) at one end, and those with a sharply 

 differentiated calyx (sepals) and corolla (petals) at the other. Between 

 these two extremes there will be found flowers with inconspicuous 

 bracts, those with bracts more distinctly perianth-like in arrangement, 

 those with a perianth differing in texture from bracts but not differen- 

 tiated into two sets. It is evident that this series may have developed 



