THE FLOWER 245 



the arrow (fig. 70, i) without being removed with the 

 mass of pollen adhering to it, as is shown in fig. 70, 3. 

 At first this mass of pollen stands upright, but in a few 

 minutes it bends forward (fig. 70, 3). The same thing 

 happens to the pollen mass adhering to the insect. 

 When it flies off to another flower, where the same process 

 is repeated, it leans with the pollen mass exactly against 

 the viscous stigmatic surface (stg.) and leaves there part 

 of the pollen. The fact that everything actually takes 

 place in the way described above can be proved from 

 insects caught during their visitation of these flowers. 

 On their proboscis and head masses of pollen have been 

 often found adhering in considerable numbers. Conse- 

 quently, the fertilisation of such flowers cannot take place 

 without the participation of insects and resolves itself into 

 cross-fertilisation, always an advantage to the plant. The 

 importance to the plant that its floral parts should have 

 just these and not other forms becomes quite apparent. 

 Let us consider another striking example where all 

 the parts of the flower appear to be adapted to the 

 same end, i.e. to cross-fertilisation by means of insects. 

 This plant is Aristolochia. Its pale yellow flower has 

 a tubular corolla swollen into a ball at the base, expanded 

 and cut obliquely at the apex. The long ovary with a 

 number of ovules (fig. 74) passes immediately without 

 any style into a lobed stigma. Stamens without any 

 filaments and closely attached to the pistil are situated 

 right down under the stigma. The narrow tube of the 

 corolla is lined with stiff hairs pointing towards the 

 inside of the flower, as is shown on the plate (71, upper 

 section). The whole arrangement is like a mouse-trap. 

 Owing to this position of the hairs the insect easily 

 crawls inside the flower, but cannot come out again ; 

 the flower is a trap where the insect finds a stigma already 

 mature and ready for fertilisation, together with stamens 

 not yet fully developed. If the insect comes from 

 another flower it rubs pollen on the stigma. Some 



