SPERA1ATOPHYTES 
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 (Nicotiana) ; 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 
