282 BOTANY 



ovule until it penetrates to the egg-cell in the embryo-sac ; whereupon 

 the union of the sexual cells is easily effected (Fig. 71). 



To render certain the accomplishment of this Pollination, or con- 

 veyance of the pollen to the female sexual organs, special and often 

 complicated contrivances are made use of by the different Phanero- 

 gams, according to the means of conveyance upon which they are 

 dependent. 



Plants of which the pollen is carried by wind are designated 

 Anemophilous. As this method of conveyance depends upon 'the 

 chance of wind direction, an enormous amount of pollen characterises 

 wind-fertilised plants. 



Such enormous quantities of pollen are often taken up from pine forests by the 

 wind that clouds of pollen fill the air. The surface of Lake Constance in spring 

 is so thickly covered with pollen that it is coloured yellow (" the lake blooms," 

 it is then said), and in the Norwegian fiords, at a depth of 200 fathoms,, 

 the pollen of Conifers, according to F. C. Noll, forms for a time the principal 

 nourishment of the Rhizopod Sacmmina. 



The male flowers of such anemophilous plants are accordingly 

 either freely exposed to the wind in Catkins (Coniferae, Ameniaceae), 

 or the versatile anthers, as in the Grasses, depend from long, lightly- 

 swaying filaments. The pollen grains themselves do not stick together 

 but escape from the opened anthers in the form of fine powder. The 

 pollen grains of many Conifers are rendered extremely buoyant and 

 easy of conveyance by the wind by two sac-like protrusions of the 

 exine. In some anemophilous plants the pollen is discharged by 

 the sudden extension of the filaments, previously rolled up in the 

 bud (Urticaceae, e.g. Piled), or by the hygroscopic tension of the 

 anthers. The female organs are also often especially adapted for 

 the attachment of the pollen thus floating in the air. The stigmas 

 either spread out like a brush (Oorylus), or are finely feathered or 

 provided with hairs (Grasses, Walnut), or drawn out into long threads 

 (Indian Corn). In the Conifers, with freely exposed ovules, the grains 

 of pollen are caught and retained in a drop of fluid exuded from the 

 micropyle, into which they are gradually drawn as the fluid dries 

 up. In other Conifers whose ovules are concealed in the cone of the 

 female inflorescence, scale-like formations catch the pollen and conduct 

 it to the sticky opening of the young ovules. 



For the fertilisation of the higher plants, the presence of water 

 is not so essential as it is for most Cryptogams. Only a few sub- 

 merged Phanerogams make use of the agency of water for effecting their 

 pollination, and are, on that account, termed hydrophilous plants. 

 The pollen of the submerged Zostera exhibits certain peculiarities, 

 distinctly referable to the necessit}^ of effecting fertilisation under 

 water. It does not form round grains, but in their place elongated 

 thread-like filaments devoid of an exine, which, as they have the same 



