188 THE STRUCTUEE OF FLOWERS. 



ones. The lower sepals do not separate until after the upper 

 stamens have shed their pollen.* 



Though we are not in a position yet to account for all 

 such deviations from general rules, yet I think in such cases 

 as the Legiiminosce and Labiatce, and probably all irregular 

 flowers, that the rationale may with great probability be 

 assumed to be the stimulus given from without to meet the 

 extra strain which certain petals or stamens or both have to 

 sustain while supporting the weight of an insect when visiting 

 them. To meet this demand an extra supply of nutriment is 

 sent to the parts which thus require it ; and, in fact, I believe 

 the final result has thus been actually brought about by the 

 effort of the plant itself, so that it has developed parts in 

 accordance with its requirements in a manner parallel with 

 that which has obtained in the animal kingdom. 



In the case of Adoxa I would regard the above-mentioned 

 orders of development as a result of unequal distribution of 

 nutriment in order of time. Thus the apical flower receives 

 its nutriment first and develops first ; then the other flowers 

 which are placed laterally subsequently. And this order of 

 supply has affected the parts of the latter flowers in the 

 same way, so that they develop from above downwards, or 

 in a postero-anterior manner. It may be compared to a 

 three-flow^ered cyme, of which the central flower expands 

 first, and the two lower ones afterwards. 



A feature must here be noticed, though I do not think much 

 stress need be laid upon it, which botanists have called "obdi- 

 plostemony." f If a flower have one whorl of stamens of the 

 same number as the petals it is isostemonous ; of two, diploste- 

 monous ; and if the stamens of the outer whorl be opposite or 



* For a note on Adoxa, see my paper On the Origin of Floral JEstiva- 

 tions, Trans. Lin. Soc, 2nd series, Botany, voL i., p. 194. 

 t Sachs' TexUBooTc, 2nd edition, p. 601. 



