OCR Text |
Show 2G2 SUMMARY OF MEASUREMENTS. CHAP. VII. plants of the second self-fertilis d o·onoration wore crossed with poll n fro1n a plant of the same variety brought fro1n a distant garden, and other flow rs wore again self-fertilised.. Plants derived from a cross with a fresh stocir and plants of tho th inl self-forti] ised generation were thus raised. The former wore to tho self-fertilise l in weight as 100 to 22; and this cnonnous di:ffi ron 1nust be attributed. in part to tho beneficial off cts of a cro s with a frc 'h stock ancl in part to tho dot riorating o~ cts of self-fertilisa-' tion continued during throe g norations. ( 4.) lberis u1nbellata. - S odlin o·s from a crimson En;glish variety crossed by a pal -coloured variety wh1ch had been °Town for so1no p:onerations in Algiers, wero to the s lf-fertilis cl se cllino·s fro1n tho crimson variety in height as 100 to 89, and as 100 to 75 in fertility. I am urprisecl that this cross with another vari ty did not procluc a still more strono·ly marked beno11cial ffect; for some inter •rossocl plants of the cri1nson Eno·lish vari ty, put into competition with plants of the same vari ty s If-£ rtilis l during three gen rations, wero in h ight as 100 to 86, and in fertility as 100 to 75. The slightly greater difference in height in this latter case, 1nay possibly bo attributed to tho d teriorating ffects of s If-fertilisation carried on for two additional g noration . (5.) Eschscholtzia californ't'ca.-This plant offers an ahno t unique a , inasrnu h as the good effects of a cross arc onfinod to the r productive system. Intercrossod and self-£ rtilised plants of the English sto k did not differ in h ight (nor in weight, as far as was a c rtained,) in any e n ·tant manner; the self· f rtilj 'Ocl plants u nally hnsino· th aclvantao·o. So it 'h b wa ' w1t th offspring of plants of th .Brazilian stock, tri •tl in the arne n1anner. Th parent-plants, however, CIIAP. VII. TABLE C. 2G3 of tho English stock produced many 1nore seeds when fertilisecl with pollen from another plant than wh n self-fertilised; and in Brazil the 1 arent-plants were absolutely sterile unless they were fertilised with pollen from another plant. Intororossed seedlings, raised in England fro1n tho Brazilian stock, co1npared with self-fertilised seedlings of tho corresponding second generation, yield.ed seeds in number as 100 to 9; both lots of plants being loft freely exposed to the visits of insects. If we now turn to the effects of crossing plants of tho Brazi.Jian stock with pollen from the English stock,-so that plants which had been long exposed to very different conditions were intercrossed, -we flnd that the offspring were, as before, inferior in height and weight to the plants of tho Brazilian stock after two generations of self-fertilisation, but w re superior to them in the most marked manner in the number of seeds produced, namely, as 100 to 40 ; both lots of plants being left freely exposed to the visits of insects. In the case of Ipomooa, we have seen that the plants derived from a cross with a fresh stock w re superior in height as 100 to 78, and in fertility as 100 to 51, to tho plants of the old stock, although these had been intercrossed during the last ten generations. With Eschscholtzia we have a nearly parallel case, but only as far as fertility is concerned, for the plants derived from a cross with a fresh stock were superior in fertility in the ratio of 100 to 45 to the Brazilian plants, which had been artificially intercross d in England for the two last generations, and which must have been naturaU y intercrossed by insects during all previous generations in Brazil, whore otherwise th y are quite sterile. (G.) Dianthus caryophyllus.-Plants self-fertilis cl |