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Show 388 ANOJ\'L\LOUS MODES CIIAP. XI. and orgam;.87 The most remarkable fact about this tree is that in its intermediate stn.to, oven when growing ncar uoth pn.ront-spocics, it is quito sterile; bnt when the flowers become pure yellow or pmc purple they yield seed. I believe that tho pods from tho yellow flowers yield a fnll complement of seed; they certainly yield a largo number. Two seedlings miRed by 1\:Ir. Herbert from such seed 88 exhibited a purple tinge on tho stalks of their flowers; but several sccdlinp;R raised by myself resembled in every ch:wactcr tho common laburnum, with the cxccpt,ion that some of them had Tcmarkably long racemes: these seedlings were perfectly fertile. Thn,t such pmity of chn.ractcr and fertility should be suddenly reacquired from so hybritli7.od and sterile a form is an astonislting phenomenon. Tho "!{ranches with purple flowers appear at fu·st sight exactly to resemble thoRo of C. pnrpureus; but on careful comparison I found that they differed from tho pure Rpccics in tho shoots being thicker, tho leaves a little broadm·, and the flowers Rlightly shorter, with tho corolla n.nd calyx less brightly purple: tho basal part of tho standard-petal also plainly showed a trace of the yellow stain. So that the flowers, at least in tl1is instance, had not perfectly recovered their true character; and in accordance with this, they were not perfectly fertile, for many of the pods contained no seed, some pr duccd one, and very fow contained as many as two seeds; whilst nnmorous podR on a tree of the pure C. pnrpu1·e"s in my garden contained three, four, and five fine seeds. The pollen, moreover, was very imperfect, a multitude of grains being smn.ll and shrivelled; and this is; a singular fact; for, n.s we shall immcclin.tcly sec, tho pollen-grn.ins in the dingy-red and st ·rile flowers on the parent-tree, were, in external appearance, in a much ucttcr stn.tc, and included very few shrivelled gmin. Although tho pollen of the reverted purple flowers wn.s in so poor n. condition, the ovules were well-formed, and, when mature, germinated freely with me. Mr. Horhert n.lso raised plants from seeds of the reverted purple flowers, and they differed very little from the usnn.l state of C. purpuTeus; but this cxprc~-; sion shows that they had not perfectly recovered their proper character. Prof. CaRpn.ry hn.s examined the ovules of tho dingy-red and sterile floWl'l'S in several plants of 0. atlrJmi on tho Continent,~9 and finds them generally monstrous. In three plants examined by me in England, tho ovules wore likewise monstrous, the nucleus varying much in shape, n.nu projecting inogularly beyond the proper con.ts. The pollcn-gmins, on the otl10r hand, judging from their cxtcmal appon.rance, were rcmn.rkauly gootl, n.nd readily protruded their tubes. By Topcatcdly counting, nndcr the microscope, tho proportional number of bad grains, Prof. CaRpm·y asc rtain d that only 2·5 per cent. were bad, w1tich is a less proportion than in tho; pollen of tluce pure species of Cytisus in their cultivated state, viz. a. pm]mreus, labnmum, and alpinus. Although the pollen of a. adami is thus in appcn.mnco goocl, it docs not follow, n.ccorcling ~7 For analogous facts, see Brnnn, ' lll'juvl'ncsrellcr.,' in 'Hay Soc. Bot. 1\Trm.,' 18:-iH, p. 3~0; anu 'Garu. Citron.,' 1!H2, p. ::97. 88 • Juur11aL of llort. Soc.,' vol. ii., 1817, p. 100. 8~ Sr'e ' 'l'ransrtet. of llort. Congress of Amsterdam,' 1805; but I owe mo~lof tlto following iuformation to Prof. Cnsp: try's letters. CJTAP. XI. OF REPRODUCTION AND V ARI.A.TION. 389 to M .. Nau?in's observations 90 on Mirahilis, tbn.t it would bo functionally effective. Tho fn.ct of the ovules of C. adami being monstrous, and tho pollen apparently sound, is all the more remarkable, bccn.usc it is opposed ~o what usually occms not only with most hybrids,91 but with two hybrids m the same genus, namely in (/. pmpnreo-elongatus, n.nd a. alp£no-laburnum . In both these hybrids, the ovules, as ob ·crvcd by Prof. Caspary and myself, were wcll-form~d, wl;ilst many of the pollen-grains were ill-formed; in the latter hybr1d 20·3 per cent., n.nd in the former no less thn.n 84·8 per cent. of t~~ gmins were ascertained by Prof. Caspn.l'y to be bn.d. This unusnal condttwn of the malo and female reproductive clements in 0. arlami has ?oc~ used by P1:o~. On. ·pary ~s n.n argument against this plant being cons1dmcd as a~ ordinary hybnd produced from seed; but wo should Temcmbor that w1th hybrids the ovules have not been examined nearly so frcq~ontly as the pollen, and they may be much oftener imperfect than is gc~mall~ su~poscd. . Dr. E. Bo~·nct, of Antibcs, informs me (through Mr.~· Tmhome Moggrrd~e) ~hat w1th hybrid Cisti the ovarium is frequently ~efOimcd, the ov:~les _bemg m some cases quite absent, and in other cases men.pn.blo of fertllisatwn. Sevcr~l theories have been propounded to account for the orlgJn of a. adu~n, n.nd for the transformations which it undergoes. These transformn. tlol~s h~ve been a~tribll:tcd by some authors to simple bud-variation; but consldo.nng the Wide cliffero~ce between a. laburnum and Jmrpunms, ?oth. of ':'h10h arc n~tur~l spocws, and considering the sterility of the mtmmcdiatc forD_~, th1s ':ow may be summarily rejected. We shn.ll prcse~ tl! sec thn.t, wrth hybnd plants, two different embryos mn.y be developed wr.thm the same se?~ and cohere; and it has been supposed that a. adami might J:n.ve thus Ol'lgmatcd.. It is known that when a plant with variegated ~c~ves 1~ budded on a plam stock, tho latter is sometimes affected, and 1t rs behoved by some thn.t the laburnum has been thus affected. Thus JHr. Pmscr states 92 that a common laburnum-tree in his garden into which three grufts of tho Gytisus ptwpu,reus had been inserted, gradun.liy assumed the chn.:n..ctcr of a. aclami; but more evidence and copious details would be reqmsrte to make so extraordinary a statement credible. l\fn.ny authors maintain thn.t 0. uclami is a hybrid produced in the common ~ay b! seed, and that it _has reverted by buds to its two parent-forms. N.~gat~ ve r~sults are of little value; but Reisseck, Caspary, and I myself, tncd ill :am to cross a. labnmum and pU?'JIUTeUS; when I fertilised tho former w1th pollen of the latter, I had the nearest approach to success for pods were formed, but in sixteen dn.ys after the withering of the flower~ th.cy fell off. ~cvcrthelcss, the belief that a. adami is a spontaneously p10duccd byb.nd between these two species is strongly supported by the faet thn.t hybnds between these species and two others have spontaneously 90 'Nouvelles Archives du Museum' tom. i. p. 143. ' 91 See on this bead, Naudio, idem, p. 141. 92 The statement is believed by Dr. Lindley in 'Gard. Chron.,' 1857, pp. 382, 400. |