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Show 208 NICOTIANA TABACUM. CHAP. VI. were of nearly equal height, and were greatly superior to their crossed opponent~. Four flowers on each plant were fertilised with their own p ,nen, and four others on the same plants were crossed with pollen from one of the crossed plants growing in another pot. This plan differs from that before followed, in which seedlings from crossed plants agajn crossed, have been compared with seedlings from self-fertilised plants again selffertilised. The seeds from the crossed and self-fertilised capsules of the a,bove two plants were placed in separate watch-glasses and compared, but were not weighed; and in both cases those from the crossed capsules seemed to be rather less numerous thqn. those from the self-fertilised capsules. These seeds were planted in the usual manner, and the heights of the crossed and selffertilised seedlings, when fully grown, are given in the preceding and following table, .LXXXVI. and LXXXVII. The seven crossed plants in the first of these two tables average 95 · 25, and the seven self-fertilised 79 · 6 inches in height; or as 100 to 83. In half the pots a crossed plant, and in the other half a self-fertilised plant flowered first. . We now come to the seedlings raised from the other parentplant B. TABLE LXXXVII. Nicotiana tubacum (Third Generat'ion). Seedlingsfrom the Self-fertilised Plant B in Pot Ill., Table LX X XV., of the last or Second Generatz'on. From Self-fertilis1·d From Self-fertilised Plant again srlf-fnti- No. of Pot. Plant, crossed by a lised, f .. rming the Cro sed Plf:tnt. Third c·lf·fertilised Gcneratiou. Inches. Inches. I. 87 ~ 72! 49 14g II . . 98~ 73 0 110~ - - III. 99 106~ 15~ 70~ -- IV. 97 ~ 48~ - -- V. 48~ 8q 0 61§ Total in inches. 495·.50 641 •75 CHAP. VI. CROSSED AND SELF-FERTILISED PLANTS. 209 The seven crossed plants (for two of them died) here average 70 · 78 inches, and the nine self-fertilised plants 71 · 3 inches in height; or as 100 to barely 101. In four out of these five pots, a self-fertilised plant flowered before any one of the crossed plants. So that, differently from the last case, the self-fertilised plants are in some respects slightly superior to the crossed. If we now consider the crossed and self-fertilised plants of the three generations, we find an extraordinary diversity in their relative heights. In the first generation, the crossed plants were inferior to the self-fertilised as 100 to 178; and the flowers on the original parent-plants which were crossed with pollen from a distinct plant yielded much fewer seeds than the self-fertilised flowers, in the proportion of 100 to 150. But it is a strange fact that the self-fertilised plants, which were subjected to very severe competition with the crossed, had on two occasions no advantage over them. The inferiority of the crossed plants of this first generation cannot be attributed to the immaturity of the seeds, for I carefully examined them ; nor to the seeds being diseased or in any way injured in some one capsule, for the contents of the ten crossed capsules were mingled together and a few taken by chance for sowing. In the second generation the crossed and self-fertilised plants were nearly equal in height. In the third generation, crossed and self-fertilised seeds were obtained from two plants of the previous generation, and tho seedlings raised from them differed remarkably in constitution; the crossed in the one case exceeded the self-fertilised in height in the ratio of 100 to 83, and in the other case were almost equal. This difference between the two lots raised at the same time from two plants J growing in the same pot, and treated in every respect alike, as well as the extraordinary superiority of the self-fertilised over the crossed plants in the first genera,tion, considered together, make me believe that some individuals of the present species differ to a certain extent from others in their sexual affinities (to use the term employed by Gartner), like closely allied species of the same genus. Consequently if two plants which thus differ are crossed, the seedlings suffer and are beaten by those from the self-fertilised flowers, in which the sexual elemeuts are of the same nature. It is known* that with our domestic animals ~ I have given evidence on th1s head in my 'Variation of Animals and Plants under Do-mestication,' chap. xvhi. 2nd eJit. vol. ii. p. 146. p |