thp: shapes of flowers. 155 



corresponding size wliich settle as bees and butterflies settle, 

 its parts will not be affected in tbe alleged manner. Thai 

 all anomalies of this kind can at once be satisfactorily ex- 

 plained, is scarcely to be expected : the circumstances of 

 each case have to be studied. But it seems not improbable 

 tbat they are all due to causes of tbe kind indicated. 



§ 235. "VVe have already glanced at clusters of flowers 

 for the purpose of considering their shapes as clusters. We 

 must now return to them to observe the modifications under- 

 gone by their component flowers. Among these occur illus- 

 trations of great significance. 



An example of transition from the radial to the bilateral 

 form in clustered flowers of the same species, is furnished by 

 the cultivated Geranimus, called by florists Pelargoniums. 

 Some of these bearing somewhat small terminal clusters 

 of flowers, w^hich are closely packed together, with their 

 faces almost upw^ards, have radially-symmetrical flowers. 

 But among other varieties having terminal clusters of which 

 the members are mutually thrust on one side by crowding, 

 the flowers depart very considerably from the radial shape 

 towards the bilateral shape. A like result occurs rmder 

 like conditions in Rhododendrons and Azaleas. The Verbena^ 

 too, furnishes an illustration of radial flowers rendered 

 slightly two-sided by the slight tw^o-sideness of their rela- 

 tions to other flowers in the cluster. And among the Cruci- 

 force, a kindred case occurs in the cultivated Candytuft. 



Evidence of a somewhat different kind, is offered us by 

 clustered flowers in which the peripheral members of the 

 clusters differ from the central members ; and this evidence 

 is especially conclusive where we find allied species that do 

 not exhibit the deviation, at the same time that they do not 

 fulfil the conditions under which it may be expected. Thus, 

 in ScaUosa succisa, Fig. 250, which bears its numerous small 

 flowers in a hemispherical knob, the component flowers, 

 similarly circumstanced, are all equal and all radial; but in 



