328 RET. O. HENSLOW OX THE STRUCTURE OF MEDICAGO SATITA. 



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by distention of the cells on the convex side or a corresponding 

 emptying of those on the concave, as no apparent diflference conld 

 be detected either in the relative size of the cells or in the amount 

 of moisture they relatively contained ; for they all presented a 

 similar appearance : hut it is possible to examine them only after 

 the tube has become curved ; for the moment it is liberated from 

 the petals, it instantly assumes that form. Possibly some such 

 arrangement as the above may exist while it is in the horizontal 

 condition, thereby retaining a state of unstable equilibrium, which 



itantly 



tube 



pistil, which may be severed from the receptacle without any 

 displacement of the stamens by passing a scalpel through the 

 enlarged orifice at the base of the slit on the upperside. On the 

 other hand, if the pistil be subsequently removed, i. e. after the 

 stamens are freed, it will be found to exhibit no elasticity or even 

 tendency to become curved. Simultaneously with the erection of 

 the stamens, and in consequence of the superior processes of 

 the alse being displaced, the alae and carina immediately drop down, 

 firmly locked together, and give that peculiar "gaping" appearance 

 not uncommon amongst papilionaceous corollas. The petals of the 

 carina also possess a strong inherent tendency to diverge and to 

 become horizontal. This tendency seems to aid considerably the 

 uprising of the stamens. 



.With regard to hive-bees sucking the nectar from the flowers 

 of Medicago sativa, they were frequently visited by them, but in 

 no instance could I find that they had power enough to set free 

 the staminal tube. N'o opportunity of observing bumblebees 

 presented itself 



The peculiar property of the ejection of the stamens is common 

 to all other species of Medicago that I have observed. 



The natural inference that one would draw from the above- 

 described structure of the stamens is, that it is in some way pur- 

 posed to secure the intercrossing of distinct flowers ; and obscr- 



Medicago 



Darwin 



'* I covered a number of plants with a net (which I know does not injure thoir 

 seeding), and left others close by uncovered, and these were visited incessantly 

 by bees. I could not oompare their relative fertility with accuracy, on account of 

 the easy shedding of the seed ; but I gathered 150 not quite ripe pods of both ; 



bees 



101 grains. No doubt the difference in the weight of the seed would have been 

 considerably greater, as the pod is formed independently of the number of seeds. 



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