1894.] Species of Medicago L. in England. 147 



The flowers of M. sativa exhibit no sleep movements ; and 

 Plusia gamma, which I have observed visiting the flowers at 9 p.m., 

 may be taken as evidence of night visitors. My hours of observa- 

 tion were between 6 a.m. and 9.15 p.m. 



M. falcata L. 



I find in this flower nothing but a yellow image of M. sativa, 

 with a distinct scent and in which, as Miiller points out, the flowers 

 become more explosive. This greater explosiveness is determined 

 by warmth as in M. sativa, but is carried to such an extent that 

 the settling of an insect must explode it, for the combining processes 

 allow the stamens half to escape. The basal-processes then no 

 longer touch each other, and some Syrphidae or even Anthomyidae 

 may reach the honey at the risk of an explosion. Heating a 

 flower brings on this very explosive stage. In the very explosive 

 state a shower of rain (as may easily be demonstrated with a 

 watering-can) causes explosion. 



Before the flower passes into this state it is impossible for any 

 common British insect (except perhaps some moths) to explode the 

 flower by merely resting on the alae. 



From plants grown in the Cambridge Botanic Gardens I 

 obtained the following figures, using wire weights as given above. 

 Average weight required to explode the flower 1'48 grammes, 

 maximum and minimum 2*46 and '60 grammes. 



The duration of the flower is slightly less than that of M. 

 sativa. 



Insect-visitors. My list of visitors is small, the plants not 

 flowering well. 



Hymenoptera aculeata : — 1. Apis mellificaJj $. 2. Bom- 

 hus hortorum L. 3. Formica rufa L. Terebrantia : — 4. Cryp- 

 tus analis Gr. ? 



Diptera: — Syrphidae: — 5. Syjphus halteatus 'Deg, 6. S. 

 luniger Mg. 7. Syritta pipiens L. 



M. prostrata Jacq. 



This flower is like the last in mechanism, but is smaller and 

 explodes when weights are hung on the alae more readily. Average 

 '53, extremes "81 and "33 grammes. 



M. silvestris Fries. 



The flowers are green, and their colour acts on a photographic 

 plate only in the same degree as the leaves of the plant. Urban ^ 

 has placed this plant under M. falcata, but, if the method of ferti- 



1 Prodromus, loc. cit. p. 56. 



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