1894.] Species of Medicago L. in England. 143 



cata L. and M. silvestris Fries ; but here I use M. sativa to signify 

 the segregate and not the aggregate species, 



M. sativa L. 



Mechanism. The flower is typically Papilionaceous, always 

 (and in this respect very different from M. maculata Sibth.) 

 with the vexillum standing above and the carina below. The 

 carina and alae are firmly united together by the usual combining 

 processes at 5 mm. from the base of the flower. The total length 

 of the alae averages about 9 mm., and of this 4 mm. belongs to the 

 claw. Further each ala possesses a basal-process 2 mm. long ; 

 and these basal processes of the two alae project towards the base 

 of the flower, lying almost parallel above the stamens. 



The stamens are diadelphous and on either side of the upper 

 free stamen at the base of the flower lies a passage — 1 mm. long — 

 giving access to the honey secreted inside the staminal tube. 

 Beyond these passages the edges of the free stamen do not merely 

 touch those of the other fused nine, but fit into grooves along 

 their margin. This is plainly seen in a transverse section of the 

 sexual organs. The explosive action of the flower depends on 

 the uppermost stamens of the fused nine, as Delpino first and 

 Miiller afterwards shewed ; these by having the cells of their 

 filaments intensely turgid tend to make the whole staminal tube 

 assume a curved form, whereby stigma and anthers are forced 

 against the vexillum. This explosive force is resisted by the 

 paired combining processes of the alae and carina, and 

 according to my observation not by the basal processes of the 

 alae : for working carefully I have at various times and under 

 various atmospheric conditions found it quite possible not only 

 to remove both these basal processes, but further to cut the claws 

 of both alae ; and in consequence of this no other resistance 

 remained to prevent the flying up of the staminal tube, except 

 that of the combining processes. Further these combining pro- 

 cesses are fixed exactly where required : — the sexual organs extend 

 to a length of 8 mm. ; after explosion there is no curvature, 

 observed in the basal 2 mm.* or in the terminal 3 mm., but 

 the bending is greatest at a point about 4 mm. from the base — 

 or just short of where the combining processes press on the 

 stamens. I see in the basal processes nothing but two 

 triggers by which the flower is, as it were, fired-off. 



The surface of the alae on both sides is covered with papillae 

 affording a good foot-hold to any insect visitor. The carina is 

 perfectly smooth, but on the inner surface of the vexillum along 



1 Therefore the nectar-passages cannot be of any use in allowing, as Henslow 

 suggests, a free curvature of the staminal tube. Note on the structure of Medicago 

 sativa. Journ. Linn. Soc. (Bot.) ix. p. .829, 1867. 



