450' VEGETABLE PHYSIOLOGY 



insects. The Plantains also afford instances of the replace- 

 ment of the one method by the other. 



Aneraophilous flowers exhibit certain structural features 

 which are associated with their mode of transference of 

 the pollen. It is produced in such flowers in great abun- 

 dance, is extremely light and dry, and in some cases is 

 furnished with bladders to aid its transport. The receptive 

 organ is in some cases a bulky cone, the leaves of which 

 are separated from each other, and from the common axis, 

 by spaces into which the pollen may drop. In others it is 

 a much-divided or plumose stigma, often furnished with 

 hairs, so that pollen falling on it may be readily retained. 

 The method, however, is a wasteful one and involves the 

 production of a superabundance of pollen. On the other 

 hand anemophilous flowers are always inconspicuous and 

 of a comparatively humble type. 



Flowers which are pollinated by insects are usually 

 much larger and more showy ; they not infrequently possess 

 irregular corollas, and are often very highly coloured and 

 provided with characteristic odours. Their perianths, and 

 sometimes their sporophylls, are highly modified to adapt 

 them to the habits of their insect visitors. As a further 

 attraction to the latter they usually produce honey in some 

 part of the flower, the nectary, in such a situation as will lead 

 to the removal of pollen by the insect in its search for the 

 attractive liquid. The markings on the coloured perianth 

 leaves are often arranged in such a way as to direct the insect 

 towards the spot where the honey is concealed. The pollen 

 itself also is often the object of the insect's visit. Many 

 special mechanisms to secure the removal of the pollen from 

 the microsporophylland its deposition on the stigma of another 

 flower are to be met with ; indeed, almost every Natural 

 Order shows some modification of the structure of the flower 

 in this direction. The consideration of them in detail, 

 however, is beyond our present purpose. 



Something akin to cross-pollination occurs in one of 

 the Hydropterideae, a family of Ferns with an aquatic habit. 



