i.] MODES OF CHECKING SELF-FERTILIZATION. 15 



sequently incapable of fertilizing itself. In E. parvi- 

 fiorum, on the contrary, the stamens and pistil come to 

 maturity at the same time. 



Fig. 13. — Epilobium angustifolium. 



Fig. 14. — Epilobium parviflorum. 



, Let us take another case — that of certain Geraniums. 

 In G. pratense all the stamens open, shed their pollen, 

 and wither away before the pistil comes to maturity. 

 The flower cannot therefore fertilize itself, and depends 

 entirely on the visits of insects for the transference of 

 the pollen. In G. pyrenaicum, where the flower is not 

 quite so large, all the stamens ripen before the stigma, 

 'but the interval is shorter, and the stigma is mature before 

 all the anthers have shed their pollen. It is therefore 

 not absolutely dependent on insects. In G. molle, which 

 has a still smaller flower, five of the stamens come to ma- 

 turity before the stigma, but the last five ripen simul- 

 taneously with it. Lastly, in G. pusillum, which is least 

 of all, the stigma ripens even before the stamens. Thus, 

 then, we have a series more or less dependent on insects, 

 from G. pratense to which they are necessary, to G. pusil- 

 lum, which is quite independent of them ; while the size 

 of the corolla increases with the dependence on insects. 



