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Show 298 THE EFFECTS OF CROSSING crossing flowers on the same plant.* In opposition to this conclusion is the fact that a bud is in one sense a distinct individual, and is capable of occasionally or ov n not rarely assuming new external characters, as well as new constitutional peculiariti s. Plants raised from buds which have thus vari cl may be propagated for a great length of time by grafts, cuttings, &c., and soinetimes even by seminal g neration. t There exist also numerous species in which tho flowers on the same plant differ from one another,-as in the sexual organs of 1nonmcious and polyo·amous plants,--in the structure of the circumfer ntial flow rs in many Compositm, Uinbelliferm, &c.,-in the structure of the central flower in some plants,-in the two kinds of flowers produced by cleistogone species,- and in several other such cases. These instances clearly prove that the flowers on the same plant have often varied iudopend ntly of one another in many important respects, such variations having been flxed, * It is, however, possible tl1at the stamens which differ in length or construction in the same flower may produce pollen differing in nnture, awl in ti1is mnnner a cro::;s might be mndo effective between the seYeml flowtrs 011 the same plant. Mr. Macnah states (in a communication toM. Verlot, 'La Production des VaricteB,' ISG5, p. 42) tllat seedlings raised from the shorter and longer stam ·ns of rhododendron differ in C'ha1acter; but the shorter stnrneni:l apparently are bec~rning rudimentary, nnd the soedllll~:s are tlw::~rfs, !:>O that ti1e l'Osult rnay be simply duo to a want of fertilit::inrr power in the pollen, as in tho <~tse of tho clwnrfcd phmts of Mirn.bilis mist•d by Nawlin by tho usc of 1oo few pollen-grains. Analogow~ stute-menta have been made with resp ct to the stamens of Pelflrgonium. With some of the Melnst() macrro, Bocdlings rai~ed by me froru tlowcr:s ferti li:;ccl by pollen from tho ~horkr stamc•ns, certninly diflorC'cl in flppenrance from tl10:su raised from tho longer !ltamcii ·, with d ifl'OIClltl)' coloured anthon~ ; but h er o, ogain, tbere is son1e reason for believing tlw.t tho shortPr st:unons are tending townrds al,ortion. In tile very diff -rent case of trimorpl1ic l1 ctero~ tyl c d plants, t1H• two sets of stamc ·Hs in ti1e sn,mc flower havo wiuoly diHcrrnt fertilising powers. t I l1ave given numerous case:l of such b11d-varialio:IS in my' Va· rintion of A11ima1s and Plants un· dor Domestication,' chap. xi. 21ld edit. vol. i. p. 448. CHAP. Vllf. FLOWERS ON THE SAME PLANT. 299 like those on distinct plants during the develop-ment of species. · It was therefore necessary to ascertain by experiment what would be the effect of intercrossing flowers on the same plant, in comparison with fertilising thorn with their own pollen or crossing them with pollen from a distinct plant. 'frials were carefully made on five genera belonging to four families; a~d in only one case, namely, Digitalis, did the offspnng fro~ a cross between. the flowers on the same plant receive any benefit, and the benefit here was s~al~ compared with that derived from a cross between distinct plants. In the chapter on Fertility, when we consider the effects of cross-fertilisation and self-fertilisation on the productiveness of the parent-plants we shall arrive at nearly the same result, namely, that a cross ?etween the flowers on the same plant does not at all Increase the number of the seeds, or only occasionally and to a slight degree. I will . now give an abstract of the results of the five trials which ·were made. (1.) Digitalis p~wp~wea.-Seedlings raised from intercrossed flowers on the same plant, and others from flowers fertilised with their own pollen, were grown in the usual1nanner in competition with one another on the opposite sides of ten pots. In this and the four following cases, the details Inay be fou~d un:ler the head of each species.. In eight pots, In wh1ch th plants did not grow much crowded: the .flow r-stems on sixteen intercrossed plants were In hmght to those on sixteen self-fertilised plants, as 100 to D4. In tho two other pots in which tho plants grew much crowde:l, tho flower-stems on nine intercrossecl plants were In heirrht to those on nino self-fertilised plants, as 100 to 9o. That the intercrossed plants in these two latter pots had a real advantao·e over their self-fertilised |
