METHODS OF POLLINATION 173 



288. Landing places for insects. Many of the flowers which 

 attract insects are irregular (those with bilateral symmetry) and 

 some portions of the flower are especially adapted to serve as a 

 landing place. This is often the lower lip of the flower, or one 

 or more of the lower petals (where more than one petal they are 



Fig. 132. 



Epi partis with portion of perianth removed to show details. /, labellum; st, stigma; 

 r, rostellum; />, pollinium. When the insect approaches the flower its head strikes the disk 

 of the pollinium and pulls the pollinium out. At this time the pollinium stands up out of the 

 way of the stigma. By the time the insect moves to another flower the pollinia have moved 

 downward so that they are in position to strike the stigma and leave the pollen. At the right 

 is the head of a bee, with two pollinia (a) attached. 



often consolidated). The keel of the papilionaceous flowers, the 

 lower lip of bilabiate flowers, the lower petal of the canna flower, 

 and the labellum of the orchids, are examples. In the violet the 

 insect rests on the two lower petals while extracting the nectar 

 from the nectary in the spur. 



289. Honey guides. Some flowers have " honey guides," 

 bright-colored lines on the petals facing the insect as it alights, 

 which lead down to the nectary. 



290. Flower structures suited to the visits of special 

 insects. Flowers with long spurs, which are formed from the 

 prolongation of one or more sepals or petals into a tube, prevent 

 most insects, except those with a long proboscis or sucking tube, 

 from obtaining nectar. The sphinx moths and humming birds are 

 visitors to many of these flowers. Examples are seen in the 

 columbine, nasturtium, etc. The outer parts of some flowers 



