496 BOTANY tart ii 



subject when floral biology is mentioned. The literature upon it is 

 proportionately large. 



What influence on floral construction can rightly be ascribed to entomophily ? 



The Gymnosperms must be excluded from consideration as purely anemophilous 

 plants. What other explanation than as an attraction apparatus in relation to 

 the world of insects in search of food can be given of the brightly coloured, i.e. not 

 green, leaves around the flower, such as the perigonial leaves, petals, bracts, or 

 spathes ? A striking example is afforded by an orchard in flower with its gleaming 

 colours contrasting in the sunlight with the general green. AVhat explanation of 

 the strong scent, increasing towards evening, of Lonicera, Philadel^yhus, etc. can 

 be given except that it serves as an attraction to night-flying insects, such as 

 Hawk-moths, which are led by the scent to find their food ? How could tlie 

 existence of nectaries, and the excretion by the plant of an important reserve food 

 substance be accounted for, if the guests which greedily consume it were not 

 indispensable to the flowers ? How, lastly, could the construction of a dorsiventral 

 flower, such as that of Salvia or of Orchis, be understood if we did not relate it to the 

 insects which visit the flower in search of nectar, and in doing so effect pollination '? 

 The mutual adaptations between the form of flowers and the bodies of insects are 

 so numerous, and the experimental fact that plants removed from their native 

 country, though growing healthily, remain sterile owing to the lack of the pollinat- 

 ing insects to which they are adapted, is so well established, that no doubt can be 

 entertained on the mutual adaptations of flowers and insects. Usually the 

 position of the nectaries is such that the hairy body of the visiting insect must 

 carry away pollen from the flower ; often the pollen will be deposited on special 

 regions of the insect's body and on another flower being visited will be deposited 

 on the stigma. It is of importance that the pollen of such entomophilous plants 

 differs from that of the anemophilous flowers described above. Pollen grains 

 provided with spiny projections, or with a rough or sticky surface, are characteristic 

 of entomophilous plants ; the grains may remain united in tetrads or in larger masses 

 representing the contents of a whole pollen sac {Orchis, Asclepias). The pollen 

 itself forms a valuable nitrogenous food for some insects such as Bees ; these form 

 "bee-bread " from it. 



In addition to the stimulus of hunger, plants utilise the reproductive instinct 

 of insects for securing their pollination. Not a few plants {Stapelia, Aristolvchia, 

 and members of the Araceae), by the unnatural colour of their flowers, combined 

 with a strong carrion-like stench, induce carrion-flies to visit them and deposit 

 their eggs ; in so doing they efi"ect, at the same time, the pollination of the flowers. 

 In the well-known hollow, pear-shaped inflorescences of the Fig (Ficus carica. 

 Fig. 532) there occur, in addition to long-styled female flowers that jiroduce seeds, 

 similar gall-flowers with short styles. In each of the latter a single egg is laid by 

 the Gall-wasp {Blaslojihacja), which in efl'ecting this pollinates the fertile flowers 

 with pollen earned from the male inflorescence (the Caprificus). The large white 

 flowers of Yucca (Fig. 452) are exclusively pollinated by the Yucca moth {Pronuha). 

 The moth escapes fi-om the pupa in the soil at the time of flowering of Yucca and 

 introduces its eggs into the ovary by way of the style ; in doing this it carries 

 pollen to the stigma. The larvae of the motli consume a jiroportion of the ovules 

 in the ovary, but without the agency of the moth no seeds will be developed, as 

 is shown by the sterility of the plant in cultivation. 



ORxrrnorniLV plays a much less important jiart tlian cntomopliih' ; the bird- 

 visitors are confined to the American Humming Birds and the Honey Birds of the 



