126 



THE STKUCTUEE OF FLOWERS, 



has to support its own weight, as will be easily understood 

 from what has been described, and by referring to the 

 diagram (Fig. 40a). 



If the tissue does not remain firm 

 nnder pressure, then the lever-action 

 of a spring may fail to be secured, 

 and the organ will oscillate freely, 

 as on a pivot. This I take to be 

 another result of a constant, but of 

 course unconscions, effort of the insect 

 Fig. 4oa.-DiagraTn of deciinate to P^^h the Organ in a Certain direc- 

 S"of fOTccs"""'^ "" *'""■ tion- It 'S thus that anthers become 

 versatile, and oscillate, and may 

 become even inverted in position, when pollination is being 

 effected by insects. Consequently anthers normally introrse 

 can be made to assume a pseudo-extrorse position. This 

 happens with some Cruciferm as Cardamine pratensis, Tulips, 

 etc. A similar cause I would attribute to the formation 

 of the oscillating anthers of Salvia, and of the species of 

 Calceolaria, as G. Pavonii, which form the 

 section Aposecos of that genus, as shown m 

 Fig. 32, a, p. 109. 



As an example of an entire flower illus- 

 trating the distribution of forces, the accom- 

 panying figure of Lamium album (Fig. 406) 

 will explain how the forms of the calyx and 

 corolla are adjusted to bear the weight of 

 the insect. The bee alights on the lip and 

 then partially crawls into the expanded 

 mouth of the corolla, so that its weight 

 now lies in the direction of w. The fulcrum will be at /, 

 and the resultant of these is in the opposite direction to r. 

 This is where the strain will be felt ; so that it is just at this 



Fig. 40b Lamium al- 

 bum, showing distri- 

 bution of forces. 



