SECT, ii PHYSIOLOGY 307 



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 necessity 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 specific weight as the surrounding water, are easily 

 set in motion by the slightest currents, and are thus brought into contact with the 

 stigmas. In the case of the submerged water plants, Vallisneria, Elodea, and 

 species of Enhalus, found in the Indian Ocean, the pollination is accomplished on 

 the surface of the water. Thus, for example, the male flowers of Vallisneria, after 

 separating from the parent plant, rise to the surface of the water, where they open 

 and float like little boats to the female flowers, which, by the elongation of their 

 spirally coiled flower-stalks, ascend, at the same time, to the surface of the water, 

 only to become again submerged after fertilisation ( 114 ). 



In the great majority of Phanerogams pollination is effected by 

 means of animals. By enticing in various ways insects, birds, bats, 

 or snails, plants are enabled not only to utilise the transporting 

 power but also the intelligence of animals in 'the service of pollen- 

 conveyance. The pollination is then no longer left to chance ; and 

 as the transport of pollen to the sexual organs becomes more assured, 

 the necessity for its formation in such enormous quantities as in 

 anemophilous plants is obviated. For the most part, such plants 

 are adapted to POLLINATION BY INSECTS (ENTOMOPHILY). For 

 their nourishment, plants offer not only the sugary sap, which, as 

 nectar, is excreted from different parts of the flowers, but also the 

 pollen itself, which furnishes a nitrogenous food material and, 

 together with the honey, is kneaded by bees into bee-bread. As 

 additional means of enticement, and to attract animals from a 

 distance to the nectar offered by the sexual organs, special perfumes 

 and conspicuous colours have also been developed. The ATTRACTIVE 

 APPARATUS of plants is generally formed by the coloured floral 

 leaves ; by the outer floral leaves or calyx (Nigella, Aconitum), or by 

 the perianth (Lily, Tulip), or by flowers specially modified for this 

 purpose (outer florets of the Compositae, Umbelliferae, and Viburnum 

 opulus ; scented flowers of Eenanthera Lowii). Bracts and portions of 

 the axis which do not belong strictly to the flower occasionally serve 

 the same function as in the circumfloral attractive apparatus of the 

 Euphorbiaceae or the extra-floral attractive apparatus of Astrantia 

 major, Salvia, Melampyrum, Dalechampia, Bougainvillea spectabilis, and 

 the Aroideae. 



The pollen of the entomophilous, in contrast to that of the 

 anemophilous plants, is not a dry powder, but its grains are stuck 

 together with an oily or mucilaginous fluid ; in other cases, they are 

 held together by their rough outer surfaces or by means of viscid 

 threads (Oenothera\ and can only be removed from the anthers by 

 animals. The structure of the flower is so contrived, as CHRISTIAN 



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