INSECTS AND FLOWERS 229 



ever, if the visits of humble-bees are delayed or prevented. 

 Lord Avebury has likened the well-known snapdragon to 

 " a strong box of which the humble-bee only has the 

 key." The flower resembles the foxglove in its general 

 plan, but the lower lip of the corolla is pressed closely 

 against the upper lip, so that small insects are quite 

 unable to force an entrance. But the burly humble-bee's 

 superior strength enables it to force its head and shoulders 

 between the jaws of the flower, and to gather nectar. In 

 so doing it gets dusted on the back with pollen, and flies 

 away to effect the cross-pollination of the next snap- 

 dragon which it visits. In the well-known monkey musk 

 (Mimulus luteus) the bilobed stigma exhibits a remark- 

 able sensitiveness. When irritated, as by the touch of a 

 bee entering a flower, the lobes of the stigma immediately 

 close together like the leaves of a book ; thus, when the 

 insect subsequently backs out, there is no risk of im- 

 mediate pollination. The stigma remains closed after 

 stimulation for several minutes, when it re-opens. " This 

 repeated opening of the stigma," writes Kerner, " is very 

 important in case the first insect visiting the flower should 

 have brought no pollen with it. Since the stigma opens 

 again, it has apparently some expectation of a second 

 visit. Should this also be unsuccessful it may open a 

 third time. The opening and closing usually continue 

 until at length an insect deposits pollen on the stigma. 

 When this happens the stigma, though opening yet again 

 for a brief period, remains permanently closed so soon as 

 the influence of the pollen is felt." The flowers of the 

 germander speedwell (Veronica ehamcedrijs) have very 

 short corolla tubes, from which the nectar can easily be 

 sipped ; but there is no alighting platform. They are 

 especially visited by small Diptera of various kinds. The 

 method by which cross-pollination is effected is described 



