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Show 406 ANEMOPHILOUS PLANTS. CHAT'. X. siinilarly dusted ; and Mr. Blackley found nu~orous pollen-grains, in one instance 1200, ~dhenng to sticky slides, which were sent up t~ a height of from ROO to 1000 feet by means of a 1n te, and then uneovered by a special mechanism. It is remarkable that in these experiments there. 'v e~·o on an average · eteen times as many pollen-grains In the atmosphere nln ' c ' ,l . at the hi(Yher than at the lower levels.* onsiuenng these fact~, it is not so surprising as it at first ap~ears that all, or nearly all, the stig1nas of anomoph1lous plants should receive polle.n brought to them by mere chance by the wind. Dunng .the early part of_ summer every object is thus dusted with pollen; for Instance, I examined for another purpose the labella of a larg number of flowers of the Fly Ophrys (which is rarely visited by insects), and found on all very 1nany polle~grains of other plants, which had been caught by theu velvety surfaces. The extraordinary quantity and lightness of the pollen of anemophilous plants are no doubt b~th necessary, as their pollen has generally to be earned to the stigmas of other and often distant flowers ; for, as we shall soon see, most anemophilous plants have their sexes separated. The fertilisation of those plants is generally aided by the stigmas being of _large size or plumose; and in tho case of tho . Con~ferw, by the naked oYules secreting a drop of :fhud, as shown by Delpino. Although the number of ane- * FOl' Mr. Hassall's observA- · tions see ' Annals and Mag. of Nut. Ilist.' vol. viii. 1842, p. 10~. In the 'North American Journal of Science,' Jan. 18-1:2, thoro is an account of the pollen swept off the decks of a vessel. Riley, • Fifth R8port on the Noxious Insects of Missouri,' 1873, p. 86. Kerner 'Die SC'hutzrnittol des PollenB',, 1:-!73, p. 6. '!'his a~,th.or has also seou a lako Ill the lyiOl so ('.overed with pollun, that tlle water no Ion O'er appeared blue. MI. Blacldoy b , Exlwrimontal Re· sea.r ches on ' Hay-f'e ver, ' 18"1''3' pp. 1:12, 1-11-152. CHAP. X. QUANTITY OF POLLEN. 407 mophilous species is smal~, a~ .the author just quoted remarks, the number of Ind1v1duals is laro·e in comparison with that of entomophilous spe~ies. 'rhis holds ~ood especially in cold. and temperate regions, where Insects are not so numerous as under a warmer climate, and where consequently ontomophilous plants are less favourably situated. We see this in our forests of Coniferm and other trees, such as oaks beeches, birches·, ashes, &c. ; and in the Graminero: Oyperacem, and J uncaceffi, which clothe our meadows and swamps; all these trees and plants being fertilised by the wind. As a large quantity of pollen is wasted by anemophilous plants, it is surprising that so many vigorous species of this kind abounding with individuals should still exist in any part of the world; for if they had been rendered entomophilous, their pollen would have been transported by the aid. of the senses and appetites of insects with incomparably greater safety than by the wind. That such a conversion is possible can hardly be doubted, from the remarks lately made on the existence of intermediate forms; and apparently it has been effected in the group of willows, as we may infer from the nature of their nearest allies.* It seems at :first sight a still more surprising fact that plants, after having been once rendered entomophilous, should ever again have become aneinophilous ; but this has oceasionally though rarely oecurred, for instance, with the common Poterium sanguisorba, as may be inferred from its belonging to the Rosaceffi. Such cases are, however, intelligible, as almost all plants require to be occasionally intercrossed; and if any entomophilous species ceased to be visited by insects, it woul~ probably perish unless it were rendered * H. Muller, 'Die Befruchtung,' &c. p. 149. |