THE PEA-WEEVU 267 



pressed one against the other, so that the grub, when 

 searching for a point of attack, cannot circulate at will. 

 Let us also note that the lower pole expands into the 

 umbilical excrescence, which is less easy of perforation 

 than those parts protected by the skin alone. It is even 

 possible that the umbilicum, whose organisation differs 

 from that of the rest of the pea, contains a peculiar sap 

 that is distasteful to the little grub. 



Such, doubtless, is the reason why the peas exploited 

 by the Bruchus are still able to germinate. They are 

 damaged, but not dead, because the invasion was 

 conducted from the free hemisphere, a portion less 

 vulnerable and more easy of access. Moreover, as the 

 pea in its entirety is too large for a single grub to 

 consume, the consumption is limited to the portion 

 preferred by the consumer, and this portion is not the 

 essential portion of the pea. 



With other conditions, with very much smaller or 

 very much larger seeds, we shall observe very different 

 results. If too small, the germ will perish, gnawed like 

 the rest by the insufficiently provisioned inmate ; if too 

 large, the abundance of food will permit of several 

 inmates. Exploited in the absence of the pea, the 

 cultivated vetch and the broad bean afford us an 

 excellent example ; the smaller seed, of which all but 

 the skin is devoured, is left incapable of germination ; 

 but the large bean, even though it may have held a 

 number of grubs, is still capable of sprouting. 



Knowing that the pod always exhibits a number of 

 eggs greatly in excess of the enclosed peas, and that 

 each pea is the exclusive property of one grub, we 

 naturally ask what becomes of the superfluous grubs. 



