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Show 378 MEANS OF CROSS-FERTILISATION. CHAP. X. This is best shown by the im possi hili ty in 1nan y cases of raising two varieties of the same species pure, if they grow at all near together; but to this subject I shall presently return; also by the many cases of hybrids which have appeared spontaneously both in gardens and a state of nature. With respect to the distance from which pollen is often brought, no one who has had any experience would expect to obtain pure cabbage-seed, for instance, if a plant of another variety grew within two or three hundred yards. An accurate observer, the late Mr. Masters of Canterbury, assured mo that he once had his whole stock of seeds "seriously affected with purple bastards," by some plants of purple kale which flowered in a cottager's garden at the distance of half a mile; no other plant of this variety growing any nearer.* But the most striking case which has been recorded is that by M. Godron,t who shows by the nature of the hybrids produced that Prhnula grandijlora must have been crossed with pollen brought by bees from P. ~ffwinalis, growing at the distance of above two kilometres, or of about one English mile and a quarter. All those who have long attended to hybridisation, insist in the strongest terms on the liability of castrated flowers to be fertilised by pollen brought from distant plants of the same species.t The following case shows whilst those left to the insects produced 10,886; that i~, ale -s number by only 351; and thi.:) small inferiority is fully accounted for by the insects not having workeJ during some days, when tl1e weather wa.s cold w1th continued rain. * Mr. W. C. Marshall caught no less than seven specimens of a moth ( Cucullia ?tlnbratica) with the pollinia of the butterfly-orc!Jis (Habena'da chlorantha) sticking to their eyes, and, therefore, in tho proper position for fcrtil.ising the flowers of this species, on an island in Derweutwatcr, at the distance of lwJf a mile from any place where this plant grew : 'N tttlne,' 1872, p. 393. , t 'Revue des Sc. Nat. 1875 ' p. 331. k t See for instn,nce the remar 8 ) l 1' j I by Horb(~rt, ' Amaryl ~~ace~,', 1837, p. 349. Also ?artn ?Ic~ strong expressions on tins ~ub~e in hi:3 ' Bastardorzeuguug, IH49' p. u70 ; aud ' Kcnntniss der Be· CHAP. X. MEANS OF CROSS-FERTILISATION. 379 this in the clearest manner : Gartner, before he had gained much_ experience, castrated and fertilised 520 flowers on various species with pollen of other genera or other species, but left them unprotected ; for, as he says, he thought it a laughable idea that pollen should be brought from flowers of the same species, none of which grew nearer than between 500 and 600 yards.* The result was that 289 of these 520 flowers yielded no seed, or none that germinated ; the seed of 29 flowers produced hybrids, such as might have been expected from the nature of the pollen employed; and lastly, the seed of the remaining 202 flowers produced perfectly pure plants, so that these flowers must have been fertilised by pollen brought by insects from a distance of between 500 and 600 yards.t It is of course possible that some of these 202 flowers might have been fertilised by pollen left accidentally in them when they were castrated; but to show how improbable this is, I may add that Gartner, during the next eighteen years, castrated no less than 8042 flowers and hybridised them in a closed room; and the seeds from only seventy of these, that is considerably less than 1 per cent., produced pure or unhybridised offspring.t fruchtung,' 1844, pp. 510, 573. Also Lecoq, 'De la Fecondation,' &c., 1845, p. 27. Some statements have been published during- Jate years of the extraordinary t en< J.ency. of hybrid plants to revert to thmr parent forms· but as it is not said how the flowers were protected from insects, it may be sus~~cterl that they were often fertllJsed with poll en brou()'ht from. a distance trom the pare~ltspecies. * 'Kcnntn:ss der Befruchtuno· ' pp. 539, 550, 575, 57G. rl' t H enschel's experiments (quoted by Gartner, 'Kenntniss,' &c., p. 574), which are worthless in all other respects, likewi:;e show l10w largely flowers are int ercrossed by insects. He castrated many flowers on thirtyseven species, belonging to twentytwo gene!·a, a11d put on their stigmas eith er no pollen, or pollen from distinc·t g-enera, yet they all seeded, and all the seedlings raised from them were of co m·se pure. :): 'Kenntniss,' &c. pp. 555, 576. |