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 offen 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 
Hydropteridee, 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 
