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Show 404 ANEMOPHILOUS PLANTS. CHAP. X. against their enemies ; but I ~ave never seen a~y reason to believe that this is so with the throe speCies observed by me, namely, Pru~us la_urocerasus, Viaia sativa, and V. jaba. No plant IS so httle attack eel by enemies of any kind as the common bracke~-fern ( Pter·is aquilina) ; and yet, as my son Francis has discovered the laro-c glands at the bases of the fronds, but only ~·hilst y~ung, excrete much sweetish ~uid, which is eagerly sought by innu1nerable ants,. eluefiy belonging to Myrmica ; and these ants certainly. <lo not serve as a protection against any enemy. Delp1no argues that such glands ought not to be considered as excretory, because if they wore so, they would Le present in every species ; but I cannot see much force in this argun1ent, as the leaves of some plants excrete suo-ar only during certain states of the weather. 'fhat b . in so1ne cases the secretion serves to attract Insects as defenders of tho plant, and may have been developed t o a high degree for this special purpose, I have not the least doubt from the observations of Delpino, ' . and 1nore especially fron1 those of Mr. Belt ~n Aaaa~a sphmrocephala, and on passion-flowers. ~his acacia likewise produces,' as an aclditional attraction to ants, small bodies containing 1nuch oil and protoplasm, and analogous bodies are developed by a Cecropia for t~o same purpose, as described by Fritz Muller.* The excretion of a sweet fluid by glancls seated outside of a flower is rarely utilised as a means for cross-fertilisation by the aid of ins cts; but this occurs with tho bracteoo of the Marcgraviacem. as tho late * Mr. Bolt ha.s given a most interesting account (' 'l'he N atumlist in Nicaragua,' 1874, p. 218) of the paramount importance of an t ::; as defenders of the above Acacia. With respect to the Ce-cropia, sec 'Nature,' 1S7q, P· 304. My son Francis has descnbed the microscopical structme m~d development of those wonderf~ll foodLodios in a paper read before the Linnen.n Society. CHAP. X. QUAN'ITrY OF POLLEN. 40:) Dr. Criige_r informed me frmn actual observation in the West Indies, and as Delpino infers with 111 uch acuteness from th~ relative position of the several parts of their flowers.* Mr. Farrer has also shown t that the flowers of ?~ronilla are c~riously ~odified, so that bees may fertilise them whilst suclnng the fluid secreted from the outside of the calyx. It further appears probable fro~ the observations of Rev. W. A. Leighton, that the fluid so abuncl~ntly secr.eted by glands on the phylloclia of the A ustrahan Acac~a magnifica, which stand near the flowers, is connected with their fertilisation.:j: 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. ~assail found that the weight of pollen produced by a Single plant of the bulrush (Typha) was 144 grains. Bucketfuls of pollen, chiefi y of Ooniferm and Graminero, have been swept off the decks of vessels near the North American shore ; and l\fr. li,iley has seen the ground near St. Louis, in Missouri, covered with pollen, as if sprinkled with sui ph ur ; 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 * 'Ult. Osservaz. Dicogamia,' 1868-ti9, p. 188. t 'Nature,' 1874, p. 169. t 'Annal::; and Mag. of Nat. Hist.' vol. x vi. 18G5, p. 14:. In my work on the ' Fertili at ion of Orchid:s,' and in a paper subsequently published in the 'A n11als nnd Mag. of Nnt. History,' it hns been shown that alt llou\)·h certain ·kinds of orchids posso;:-s ~nectary, ~o nectar is actu a lly scCJ·ctod by ~t; but that insects penetrate the Inner walls and suck tho flu id contained in the intercellular spaces. I further suggested, in tlte case of some other oreltids which do not sel'rete nectar, that insect::; gnawed the lal>ellun1; and this suggestion llas since been proved true. H. Mliller and Delpino have now shown tl1at some other plants have thickened petals which :tre sucked or gnawed by in ects, their f(;rtili:salion bdng thus aiJcd. All the kuown facts on this head llave been collected by Delpino in his 'Ult. Osserv.' part ii. fasc. ii. 1875, pp. 58-63. |