SPERMATOPHYTES 



253 



in either direction; that is, either by the gradual reduction and final 

 elimination of the perianth (a reduction series), or by the gradual ap- 

 pearance and differentiation of the perianth (an ascending series). In 

 the one case the naked flowers, for example, would be reduced flowers ; 

 in the other case they would be primitive flowers. There is every reason 

 to believe that evolution has taken place in both these directions, and 



Figs. 563-565. — 563, sympetalous flower of tobacco (N icotiana) ; 564, an opened 

 corolla tube, showing the stamens apparently attached to it; 565, the syncarpous pistil. 

 — After Strasburger. 



that what are known as simple flowers are sometimes primitive and 

 sometimes reduced. 



Spiral to cyclic. — A very evident tendency in the evolution of the 

 angiosperm flower is to pass from what is called the spiral condition 

 to the cyclic condition. In a strobilus the bracts and sporophylls are 

 spirally arranged upon a more or less elongated axis, and are indefinite 

 in number ; and this same condition occurs in the flowers of certain 

 angiosperms. Beginning with this strobilus-like flower there is a ten- 

 dency to shorten the floral axis (receptacle), which results in a closer 

 spiral of flower parts, and finally reaches the cyclic stage, in which there 

 is a cycle for each kind of organ. At the same time, the receptacle 



