130 THE STRUCTURE OF FLOWERS. 



In the preceding cases tlie regularity occurring in 

 normallj irregular flowers is due to the non-development 

 or arrest of the usually characteristic features which give 

 rise to the irregularity ; so that the resulting form is a 

 reversion to, or a restoration of, the ancestral conditions of 

 the flower which is assumed to have been perfectly regular. 



As insects, by their mechanical actions, are hei'e believed 

 to have brought about irregularities in flowers ; so, con- 

 versely, regularity can be reacquired through their agency 

 in another way. Clerodendron is a plant in the corollas of 

 which certain members of the family Tingidce take up their 

 abode as pupse. The irritation induced by their presence 

 brings about a hypertrophy of the corolla, which now 

 assumes a regular form, while the filaments and style are 

 likewise affected, becoming much thicker than in the normal, 

 irregular flower. 



Reversions to regularity may, therefore, I think, be safely 

 referred to nutrition as the immediate agent, though such 

 extra flow of nutriment may be brought about by diverse 

 causes. 



" Peloria." — Regularity may, however, arise in another 

 way, by the members of the whorl or whorls normally 

 irregular being all exactly alike. Instead of there being 

 any arrest, there is here an excess of development. Thus, 

 if, instead of the anterior petal of Linaria being the only one 

 provided with a spur, all the petals become spuiTed, then the 

 corolla will become regular ; but there is no other tendency 

 to revert to the ancestral form. This variety constitutes the 

 form called " Peloria " by Linnseus. 



There are, then, two factors, which appear either singly 

 or together, in this process of change. First, a terminal 

 position, as this tends to produce regularity in consequence 

 of an equable flow of sap in all directions : just as this also 



