THE DISPERSION OF SEEDS AND SPORES. 69 



and raost Fungi, including Lichens, depend mainly on 

 the wind for their dissemination, but show no special 

 adaptation further than minuteness, lightness, in- 

 coherence, and prodigious numbers. A further 

 provision is seen in Coniferae. Each pollen-grain of 

 Pinus is furnished with two wings formed by the 

 inflated extine — structures which must very materially 

 aid in dispersion. In one respect, however, the Cryp- 

 togams seem to have an advantage over the pine 

 and other Gymnosperms. The open carpels of the 

 Coniferse and their allies are destitute of stigmas. 

 The pollen-grain must be conveyed to the ovule, 

 and the only provision for its reception is a drop of 

 fluid exuded from the micropyle. In the absence of 

 a specialised stigma, the only guarantee that any of 

 the pollen-grains will reach their proper destination 

 is that afforded by their enormous numbers. The 

 probability of any coniferous ovule being properly 

 pollinated would be slight but for the fact that the 

 pollen is showered down everywhere, and it is next 

 to impossible for all the ovules on a cone to 

 escape. But it is improbable that every ovule will be 

 fertilised, and many which the pollen never reaches 

 must perish. From the more perfect arrangements 

 for the delivery of the fertilising cells, the oospheres 

 of Cryptogams seem to stand a better chance of 

 fertilisation than the ovules of Coniferae. The 

 pollen of the latter is passive and motionless, whereas 

 the antherozoids of the Cryptogam are not only 

 active and motile, but have the additional advantage 

 of being dispersed from secondary centres, as will be 

 explained presently. Wind - fertilised flowers have 

 usually an expanded feathery or penicillate stigma,, 

 exposing a relatively large stigmatic surface, and 

 increasing the flower's chances of fertilisation. At 

 the time of flowering, these expanded stigmas in- 

 tended for the reception of the pollen are fully 

 exposed. Its safe arrival is therefore an event of 

 much greater probability than the pollination of a 

 conifei'ous ovule. 



