440 VEGETABLE PHYSIOLOGY 



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, not infrequently possessing 

 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, 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 microsporophyll and its deposition on the 

 stigma of another flower are to be met with ; indeed almost 

 every Natural Order shows some modification of the struc- 

 ture 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 

 Hydropteridecz, a family of Ferns with an aquatic habit. 

 The plant in question, which is known as Azolla, is a small 

 floating organism, consisting of a horizontal rhizome, some- 

 times copiously branched, on which are borne numerous 



