840 



ECOLOGY 



with flowers ; this habit is without obvious advantage, though it has been suggested 

 that trunk flowers are well protected from torrential rains. Cauliflory appears to 

 be stimulated by an excess of moisture ; it has been induced in the grape also by 

 wounding and in the orange by defoliation. In some tropical trees and shrubs (as 

 in Ficus geocarpa) flowers break through the soil from subterranean stems. Tran- 

 sitions between wind-pollinated and insect-pollinated flowers sometimes are seen, 

 as in the ericads, where the pollen which commonly is scattered by insects ultimately 

 becomes dry and powdery and thus may be scattered by the wind ; chestnut flowers 

 which usually are wind-pollinated are fragrant and attract insects. Epfiedra cam- 



pylopoda is interesting as be- 

 ing an insect-pollinated gym- 

 nosperm, the flowers, which 

 are much frequented by in- 

 sects, exhibiting nectar and 

 sticky pollen which coheres 

 in masses. Before consider- 

 ing in detail the features 

 that attract insects to flowers, 

 it is necessary to consider 

 the pollinating organisms 

 themselves. 



Pollinating insects. 



General remarks. The 

 vast majority of efficient 

 FIGS. 1166-1169. Flowers of Salvia, illustrating pollinating animals are 



pollination by bees: 1 166, a flower of Salvia glutinosa .in j n particularly fly- 



longitudinal section, the arrow indicating the direction 



taken by visiting bees; s, style; a, anther; n67,asimi- ln e> insects, Since those 

 lar section, showing the lower arm of the connective 

 lever pushed back, as by an entering bee, the pollen- 

 bearing anther (a) thus being deflexed in such a way as 

 to rub pollen over the insect; 1168, a Salvia flower into 



which crawl from flower 

 to flower are likely to 

 brush off most of the 



Among 

 insects those 



which a bee has entered, the anther (a) being in contact pollen en route. 



with the bee; 1169, an older flower, showing the stigma ,1 a 



(g) in such a position as to come into contact with an *. 



entering bee; 1 168 and 1 169 show that Salvia is protan- that visit flowers regU- 



drous. 1166 and 1167 from KERNER; 1168 and 1169 larly for nectar or pollen 



from AVEBURY (LUBBOCK). ,, . . 



are the most important. 



Flowers with exposed nectar and pollen are visited by most of the 

 flower-frequenting species, but flowers with hidden nectar or pollen, 

 especially those with long corolla tubes or whose nectar accumulates 

 in long spurs (fig. 1171), are pollinated only by highly specialized in- 

 sects with elongated mouth parts. 



Bees. The most important pollinating insects belong to the Hymen- 

 optera, a group which includes the bees, wasps, and ants. The honey- 



