106 THE STRUCTURE OF FLOWERS. 



If no more than the head of an insect enter the flower, 

 then the corolla shapes itself to fit it. Thus Snowberry, 

 Scropliularia, and Bpijpactis only admit the heads of wasps, 

 which are the regular visitors of these plants. 



Other instances in which the limb is not much, if at all, 

 enlarged occur in flowers especially adapted to Lepidoptera. 

 Hovering, as they generally do, before the flowers, and in- 

 serting their long proboscides while on the wing, there is no 

 tendency to develop larger anterior petals, but the irritation 

 affects the tube only, which thus elongates and contracts, 

 resulting in little or no irregularity in the flowers, as in 

 (EnotTiera biennis, in which the calyx tube has contracted, or 

 in Honeysuckle, which has a tubular corolla. If bees or 

 other insects visit the flower as well, then some degree of 

 obliquity may result, as in Teucriwm Scorodonia. 



Thus, then, may we get a rationale of the structure and 

 form of floral organs, and their great diversity corresponds to 

 a similar diversity in the insect world ; for the flower, if it 

 be visited by many, will presumably take a form correspond- 

 ing to the resultant of the forces brought to bear upon it ; 

 if visited by few, it will shape itself in accordance with the 

 requirements of its principal visitors ; and thus is it that 

 while some easily accessible flowers receive many classes of 

 insects, others are restricted to few, or even one ; and then 

 the insect and the flower are so closely correlated as to almost 

 impress upon one the idea that they were mutually created 

 for each other ! 



The accompanying figures of Duvernoia adhatodoides * 

 may illustrate my meaning. Looking at Fig. 31, a, alone (sup- 

 posing we know nothing of insect visitors), one might ask, 

 For what use is this great irregularity ? why and how has it 



* From a paper by Mrs. Barber, Journ. Lin. Soc. Bot., vol. xi., 

 p. 469. 



