144 Mr Burkill, On the Fertilisation of some [Feb. 12, 



the margin is a band of papillate epidermis, broadest at the apex 

 and narrowing downwards ; this too may afford a foot-hold to any- 

 long-legged insect. The centre and base of the vexillum are 

 perfectly smooth. 



Pollen is shed in the bud, and lies round the stamens and 

 stigma in a little lens-shaped space made by the carina. 



The stigma is at this time, as Henslow says of M. denticulata, 

 mature ^ ; but I have covered a considerable number of flowers 

 with nets to prevent insect-visits and get results agreeing with 

 those of Urban ^, i.e. no seeds are set in the unexploded flower 

 in spite of the pollen in contact with the stigma. This is explained 

 by the fact that the stigma does not become receptive 

 until rubbed or until its cells are injured in some manner. 

 My proof is I think conclusive. Firstly, the stigma appears not 

 to be moist, but when rubbed on glass leaves a sticky mark. 

 Secondly, I have caused flowers to set seed though unexploded, 

 (1) by pinching the stigma through the keel, (2) by perforating 

 the keel with a needle and scratching the stigma, and (3) by 

 cutting off the tip of the keel and rubbing the stigma with a 

 stiff paint-brush. An insect visitor exploding the flower will 

 injure the stigmatic papillae and bring about fertilisation ^ There 

 appears to be a prepotency in foreign pollen, to judge from Urban's 

 observations* on the hybridisation of M. sativa and falcata. 

 Patches of these two plants were grown by him close together; 

 and amongst the seedlings derived from them only two from 

 M. sativa and none from M. falcata proved true ; the rest being 

 the hybrid form M. media. 



Insect visitors, observed in and near Cambridge. 

 Hymenoptera aculeata : — 



1. Apis mellifica L. ^ very 2. Bomhus pratorum L. 



abundant. 3. B. lapidarius L. 



4. B. ho7'torum L. not un- 5. B. muscorum L. 



common. 6. Megachile oentuncularis L. $ 



7. Vespa vulgaris L. $ . 8. Andraena convewiuscula 



9. A extricata Smith. (^ . Kirby $. 



^ Henslow. Self-fertilisation of plants. Popular Science Eeview, New Series, 

 m. p. 13, 1879. 



'■^ Loc. cit. 



3 Seringe's variety tumida of ill. falcata, which appears from the description 

 as if it might be cleistogamic, is a gall — the work of a Gecidomyia, whose larvffi 

 mature inside the hypertrophied bud. The gall is common on M. sativa at Cam- 

 bridge. De CandoUe's Prodromus, n. p. 173. 



■* Verhandlungen d. Bot. Vereins d. Provinz Brandenburg, xix. p. 125, 1877. I 

 endeavoured by timing the rate of withering of cross and self- fertilised flowers, to 

 obtain some evidence on the question of prepotency, but failed to find anything 

 satisfactory. Only the younger flowers withered more rapidly than the older ones. 



