306 BOTANY P\KT i 



possibly the explanation is that the embryo-sac nucleus, as a sister nucleus to that 

 of the ovum, i-\nvi~r> a similar chemotactic influence, and thus attracts the male 

 generative cell, the fusion 1 icing of secondary importance since the endosperm is 

 destined to be used as food by the embryo C 1 - . 



While one healthy pollen grain should be able to fertilise one 

 healthy ovule, experience shows that better results follow from inure 

 liberal pollination of the stigma. This depends, according to 

 COKUENS, on the fact that not every pollen grain (and not every 

 ovule) is good. Thus in Mvrabttis jalapa for each fertile pollen grain 

 four are found infertile, and for every three good ovules there is one 

 bad one. For Miralills loxgijlora the corresponding ratios are 1 : 3 

 and 1 : 1 ( 3 ). 



To render certain the accomplishment of this POLLINATION, or 

 conveyance of the pollen to the female sexual organs, special and 

 often complicated contrivances are made use of by the different 

 Phanerogams, according to the means of conveyance upon which they 

 are dependent. 



Plants, the pollen of which is carried by wind, are designated 

 .\\KMOPHILOUS. As this method of conveyance depends upon the 

 chance of wind direction, the production of an enormous amount of 

 pollen characterises wind-fertilised plants. According to Holden a 

 medium-sized plant of maize produces about 50,000,000 pollen grains. 



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 

 a Rhizopod (Saccamina). 



The male flowers of such anemophilous plants are accordingly either freely 

 exposed to the wind in Catkins (Couiferae, Querciflorae), 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 exinc. In 

 some anemophilous plants the pollen is discharged by the sudden extension of the 

 filaments, previously rolled up in the bud (Urticaceae, e.g. Pilca), or by the hygro- 

 scopic tension of the anthers. The female organs are also often specially adapted 

 for the attachment of the pollen thus floating in the air. The stigmas either spread 

 out like a brush (Corylus), 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, processes of the integument 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 submerged 



