INSECTS AND FLOWERS 193 



the rostellum. Altogether, the blossom is 

 extremely complex and interesting. To under- 

 stand its mechanism, we must shrewdly watch 

 what takes place when an insect visits it. When 

 a Humble-bee alights on the labellum, which 

 from its shape and striking coloration forms a 

 peculiarly attractive alighting place, the insect 

 proceeds to push its head and proboscis into the 

 entrance to the nectary in search of honey. Now 

 the pouch-formed rostellum projects into the 

 gangway of the nectary in such a way that it is 

 practically impossible for any object to be 

 pushed into it without the rostellum being 

 touched. Consequently the insect in reaching 

 forward, brings its head against the delicate 

 outer membrane of the rostellum, which is 

 ruptured, and the pouch bearing the sticky balls 

 of the pollinia is depressed so that one or both 

 touch against the front of the insect's head, to 

 which they instantly firmly adhere, for the viscid 

 matter has a peculiar cement-like property of 

 setting hard and dry in a few seconds. The 

 result is that when the insect withdraws its 

 head from the nectary, one or both of the 

 pollinia will be withdrawn, firmly cemented to 

 the front of the head, erect and projecting like 

 horns. As the bee makes its way to another 

 flower, the pollinia alter their position through 

 the contraction of the minute disc of membrane 

 to which the stalk or caudicle adheres, so that 

 instead of standing erect, they now bend directly 

 forward toward the apex of the bee's proboscis. 

 The result of this movement is to bring the 

 pollenium into such a position that its base will 



