DISPERSION OF POLLEN BY THE WIND. 133 



distributed Vallisneria spiralis, in Vallisneria alternifolia, which is indigenous 

 in tropical Asia, in JEnalus acoroides, which grows in the Pacific and Indian Oceans, 

 in Hydrilla verticillata, Elodea Canadensis, and a few species of the genus 

 Lagarosiphon, native at the Cape and in tropical Africa — only 13 species all 

 together, comprised in the little family of Hydrocharidacese. This number is 

 almost inappreciable compared with that of the species which produce pollen in 

 the form of fine dust or loose flour, and wherein the pollen is dispersed exclusively 

 and throughout the period of flowering by the wind which blows it away in clouds. 

 It would not be far out to put the number of wind-pollinated plants at 10,000, 

 i.e. at about a tenth of the total number of Phanerogams. To this category belong 

 the Conifers, Oaks, Beeches, Hazels, Birches, Alders, Poplars, Walnut-trees, Mul- 

 berry-trees, Planes, and the majority of Palms. All these are of the nature of 

 lofty trees, and usually grow in numbers together, each being associated with 

 others of its own kind so as to form extensive woods or plantations, characterized 

 by a close association of individuals. To these must be added the Grasses produced 

 in meadows, prairies, and savannahs; the Sedges, Reeds, and Rushes characteristic 

 of marshes; the Cereals of our fields; Hemp, Hops, Nettles, and Plantains; the 

 common Pondweeds growing in still or running water, and many other plants 

 belonging to families of the most widely different kinds. 



One striking characteristic of these exclusively wind-fertilized plants is the 

 absence of fragrant and bright-coloured flowers. The floral-leaves are compara- 

 tively small, of a greenish or yellowish colour, and stand out very little, if at 

 all, from the foliage. The interior of the flower is destitute of honey and 

 perfume. It is of no advantage to these flowers to be visited by insects, and 

 accordingly they have no need of any of the means of alluring bees, butterflies, 

 or flies. Hence the absence of odorous substances, of sw^eet juices, and of 

 brightly-coloured corollas contrasting with the green foliage and visible from 

 afar. We do not mean to say, however, that the flowers of the plants in 

 question are altogether shunned by insects. Many insects covet the pollen itself, 

 and not infrequently they may be seen hovering about the catkins of Hazels 

 and Birches, on the spikes of Plantains, the panicles of Grasses, Rushes, and 

 Reeds, collecting or devouring the pollen. But these visitors play but a very 

 subordinate part in the dispersion of the pollen. By knocking against parts of 

 a flower that are covered with pollen-dust they may, of course, cause some to 

 fall out, but in so doing they only render a service to the plant if the right wind 

 happens to be blowing at the moment and conveys the pollen to the stigmas. 

 If there is no wind, or it blows in a wrong direction, the plants are more 

 likely to be injured than aided by the insects' visits; for, as the stigmas are not 

 brushed by the pollen-seeking insects and therefore receive no deposit of pollen 

 from them, and, on the other hand, the pollen that they shake out is not likely 

 to be carried to the corresponding stigmas if the air is still, it usually happens 

 that anemophilous plants of the kind thus suffer a loss of pollen without 

 ■obtaining any compensating advantage. 



