BEES AS FERTILISERS. 297 



The consideration of the movements of the fila- 

 ments of Kalmia and Arbutus Unedo naturally intro 

 duces a common British plant, whose filaments are 

 remarkably irritable, and hence often secure cross- 

 ing. In the common barberry, which, in June, 

 bears drooping racemes of yellow flowers, the six 

 filaments spread directly outwards, standing just over 

 the six petals, which bear twelve conspicuous honey 

 glands that are very alluring to bees. Should one 

 of the latter, in seeking sweets, touch a filament, 

 it immediately springs upwards, striking the insect, so 

 as not only to dust its body, but to so startle it that 

 it retires to another flower, when the pollen carried 

 off is immediately transferred to the receptive edge 

 of the upstanding stigma. So persistent is this curious 

 property, that the filament will contract upon being 

 touched after its removal from the flower. 



We have previously noticed several cases in which 

 the genders appear on different {dioecious) plants, 

 the flowers being unisexual, and, in consequence, 

 incapable of self-fertilisation ; and we have now to 

 consider a most interesting set of variations, in which 

 the flowers become practically dioecious, although 

 they remain hermaphrodite, securing cross-fertilisa- 

 tion by differentiating into two, or even three, dis- 

 tinct forms, which are complementary to one another. 

 If, by example, a handful of primroses be gathered 

 promiscuously from several plants, they will be found, 

 upon examination, to present very apparent dissimi- 

 larities amongst themselves, some having a pale green, 

 almost globular form (s, A, Fig. 61), the stigma, at 

 the top of the corolla tube, others, at the same spot, 



