With respect to the Cecropia see 'Nature' 1876 page 304. My son Francis has described the microscopical structure and development of these wonderful food-bodies in a paper read before the Linnean Society.)
The excretion of a sweet fluid by glands seated outside of a flower is rarely utilised as a means for cross-fertilisation by the aid of insects; but this occurs with the bracteae of the Marcgraviaceae, as the late Dr. Cruger informed me from actual observation in the West Indies, and as Delpino infers with much acuteness from the relative position of the several parts of their flowers. (10/51. 'Ult. Osservaz. Dicogamia' 1868-69 page 188.) Mr. Farrer has also shown that the flowers of Coronilla are curiously modified, so that bees may fertilise them whilst sucking the fluid secreted from the outside of the calyx. (10/52. 'Nature' 1874 page 169.) It further appears probable from the observations of the Reverend W.A. Leighton, that the fluid so abundantly secreted by glands on the phyllodia of the Australian Acacia magnifica, which stand near the flowers, is connected with their fertilisation. (10/53. 'Annals and Magazine of Natural History' volume 16 1865 page 14. In my work on the 'Fertilisation of Orchids' and in a paper subsequently published in the 'Annals and Magazine of Natural History' it has been shown that although certain kinds of orchids possess a nectary, no nectar is actually secreted by it; but that insects penetrate the inner walls and suck the fluid contained in the intercellular spaces. I further suggested, in the case of some other orchids which do not secrete nectar, that insects gnawed the labellum; and this suggestion has since been proved true. Hermann Muller and Delpino have now shown that some other plants have thickened petals which are sucked or gnawed by insects, their fertilisation being thus aided. All the known facts on this head have been collected by Delpino in his 'Ult. Osserv.' part 2 fasc. 2 1875 pages 59-63.)
The amount of pollen produced by anemophilous plants, and the distance to which it is often transported by the wind, are both surprisingly great. Mr. Hassall found that the weight of pollen produced by a single plant of the Bulrush (Typha) was 144 grains. Bucketfuls of pollen, chiefly of Coniferae and Gramineae, have been swept off the decks of vessels near the North American shore; and Mr. Riley has seen the ground near St. Louis, in Missouri, covered with pollen, as if sprinkled with sulphur; and there was good reason to believe that this had been transported from the pine-forests at least 400 miles to the south. Kerner has seen the snow-fields on the higher Alps similarly dusted; and Mr. Blackley found numerous pollen-grains, in one instance 1200, adhering to sticky slides, which were sent up to a height of from 500 to 1000 feet by means of a kite, and then uncovered by a special mechanism. It is remarkable that in these experiments there were on an average nineteen times as many pollen-grains in the atmosphere at the higher than at the lower levels. (10/54. For Mr. Hassall's observations see 'Annals and Magazine of Natural History' volume 8 1842 page 108. In the 'North American Journal of Science' January 1842, there is an account of the pollen swept off the decks of a vessel. Riley 'Fifth Report on the Noxious Insects of Missouri' 1873 page 86. Kerner 'Die Schutzmittel des Pollens' 1873 page 6. This author has also seen a lake in the Tyrol so covered with pollen, that the water no longer appeared blue. Mr. Blackley 'Experimental Researches on Hay-fever' 1873 pages 132, 141-152.) Considering these facts, it is not so surprising as it at first appears that all, or nearly all, the stigmas of anemophilous plants should receive pollen brought to them by mere chance by the wind. During the early part of summer every object is thus dusted with pollen; for instance, I examined for another purpose the labella of a large number of flowers of the Fly Ophrys (which is rarely visited by insects), and found on all very many pollen-grains of other plants, which had been caught by their velvety surfaces.