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Show 364 DARWINISM CHAl'. pared with tho enormous areas of sea-bottom, over ':hi?h tho atmospheric dust must have been scattm:ed, ren~le~ 1t. m the hiahest dearee improbable that the maximum bm1t mther of si;e of particles or of distance from land has been reached. Let us how~ver assume that tho quartz grains, found hy Mr. Murr~y in the deep-sea ooze 7 00 miles from land, give .n:-; the extreme limit of the power of the atmosphere ::ts a earner of solid particles, and let us compar~ with these the wei~hts of some seeds. From a, small collectiOn of the seeds of th1rty ·- I Species. Approxlm~tte Approximate Remarks. No. No. of Seed• Dimensions. in one Grain. -- in. in. in. I 1 Draba verna 1,800 2 Hypericum perforatum 520 3 Astilbe rivulari . . 4,500 4 Saxifraga coriophylla . 750 5 <Enothera rosea . 640 6 Hypericum hirsutnm . 700 7 Mimnlus luteus . 2,900 8 Penthorum scdoidcs 8,000* 9 Sagina procumbens 12,000* -i1f X T}7f X Th }7Jx -g\r -rf"Oxrh -(rr x ,lr; i1f x -lrr -:frs x rh lf\XTh -.h x rh rh Oval, flat. Cylindrical. Elongate, flat, tailed, w; 1\')'. urfacc rough, at! her' t 0 th<' dry capsules. Ovate. ylintlrical, rough. Om!, minute. Flattened, very min ute. Sub-triangular, fla t. 10 Orchis maculata 15,000 * ... Margined, flat, vrry min nit•. 11 Gentiana purpurca 35 -(r; Wavy, rough, wi th this ('lll'i-aceous margin s. 1~ Si1ene alpina ... -h Flat, with frin gc<l marg 13 Adenophora communis ... -l1f X frs Very thin, wavy, l ight. IllS, Quartz grains 25,000 ~h Deep sea 700 llli Do. 200,000 r;l1! u Genoa 600 lll i species of herbaceous plants sent me from Kew, those in the above table were selected, and small portions of eight of them carefully weighed in a, chemica,] balance.1 By counti11 ~ these portions I was able to estimate the number of seeds weighing one grain. The three very minute species, whose numbers arc marked with an asterisk (*), were estimated hy the comparison of their sizes with those of the smaller weighed seeds. If now we compare the seeds with the quartz gra.ins, we 1 I am in<lebte•l to Professor R. Meldola. of the Fins bury Technical Tustitut e, and Rev. T. D. Titmas of Charterhouse for furnishing me with the weight» required. XII GEOGRAPHICAL DISTRIBUTION OF ORGANISMS 365 find that ~everal arc from twice to three times the weight of the grams found by Mr. Murray, and others five times, eight times, and fifteen times as heavy; but they are proportionn, tcly very much larger, and, being usually irregular in shape or compressed, they expose a very much larger surface to the air. The surface is often rough, ::tnd several have dilated marains or tailed appendages, increasing friction and renderina the u~1iform rate of falling through still air immensely les~ than 111 tho ca.se of the smooth, rounded, solid quartz rrrains. With these advantages it is a moderate estimate that 0 seeds ten times the weight of the quartz grains could be carried quite as far through the air by a violent gale and under the most fa.voumble conditions. These limits will include five of the seeds heru given, as ·well as hundreds of others which do not exceed them in weight; and to these we may add some larger seeds which have other fu.vourable characteristics, as is the case with numbers 11-13, which, though very much larger than the rest, are so formed as in a,ll probability to be still more easily carried great distances by a g::tle of wind. It appears, therefore, to be absolutely certain that every autumnal gale capable of conveying solid mineral particles to great distances, must also carry numbers of sm::tll seeds at least as far ; and if this is so, the wind alone will form one of the most effective agents in the dispersal of plants. Hitherto this mode of conveyance, as applying to the tmnsmission of seeds for great distances across the ocean, has been rejected by botanists, for two reasons. In the first place, there is said to be no direct evidence of such conveyance · and secondly, the peculiar plants of remote oceanic islands clo not appear to have seeds speci::tlly adapted for aerial transmission. I will consider briefly each of these objections. Objection to the Them·y of rVind-Dispersal. To obtain direct evidence of the transmission of such minute and perishable objects, which do not exist in great quantitie , and are probably carried to the greatest dist::tnces but rarely and as single specimens, is extremely difficult. A bird or insect can be seen if it comes on board ship, but who woul<.l ever detect the seeds of Mimulus or Orchis even if a score of them fell on a ship's deck 1 Yet if but one such seed |