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Show 204 NICOTIANA TABACUM. CIIAP. VI. approximately equal; and in one (i.o., in the first generation) the self-fertilised plants were greatly superior to tho crossed. In no case did the capsules from flowers fertilised with pollen from a distinct plant yield many more, and sometimes they yielded much fewer seeds than the capsules from self-fertilised flowers. But when the flowers of one variety were crossed with pollen from a slightly different variety, which had grown under somewhat different conditions,-that is, by a fresh stock -the seedlings derived from .t~is cross exc~eded in height and ~eight those from the self-fertilised flowers In an extraordinary dogreo. Twelve flowers on some plants of the coq1mon tobacco, raised from purchased seeds, were crossed with pollen from a distinct plant of the same lot, and these produced ten capsules. Twelve flowers on the same plants were fertilised with their own pollen, and produced eleven capsules. The seeds in the ton crossed cap~~Ies weighed 31· 7 grains, whilst those in ten of tho selffertilised capsules weighed 47 · 67 grains; or as 100 to 150. The much greater productiveness of the self-fertilised than of the crossed capsules can hardly be attributed to chance, as all the capsules of both lots were very fine and healthy ones. The seeds were placed on sand, and several pairs in an equal state of germination were planted on the opposite sides of three pots. The remaining seeds were thickly sown on the two sides of Pot IV., so that the plants in this pot were much crowded. The tallest plant on each side of each pot was measured. Whilst the plants we~·e quite young the four tallest crossed plants ~verag~d 7 · 87 Inches, and the four tallest self-fertilised 14 · 87 I~ches.In height; or as 100 to 1B9. The heights at this age are given In ~he two left columns of the following table. When In full flower the tallest plants on each side were again measured (see the two right-hand columns), with the following result. But I should state that the pots were not large enough, and the plants never grew to their proper height. The four tallest ~r.ossed plants now averaged 18 · 5, and the four tallest self-fertilised plants 32 · 75 inches in height; or as 100 to 178. In all four pots a self-fertilised plant flowered before any one of the crossed. In Pot IV., in which the plants were extremely crowded the two lots were at first equal; and ultimately tho tGtllest cr~ssed ~lant exceeded b~ a trifle the tallest self-fertilised plant. This 1 ecalle.d t~ my ~.1nd an analogous case in the one generation of Petunia, In whwh the self-fertilised plants were throughout CHAP. VI. CROSSED AND SELF-FERTILISED PLANTS. 205 TABLE LXXXIV. Nicot-iana tabacum (First Generation). May 20, 1868. I December 6, 1868. I - No. of Pot. Crossed Sci f-fertHised I Crossed I Self-fertilised Plants. Plants. Plants. l)lants. ----- ~~. Inches. Inches. I. 15~ ~6 40 44 II. B 15 I 64g 43 ------------- --------- III. 8 13~ 16 33 ----- --------- --------- IV. 5 5 11~ 11 Crowded. ------------- Total in . 31·5 59•5 74•0 131•0 inches. their growth taller than the crossed: in all the pots except in the crowded one. Accordingly another trial was made, and some of the same crossed and self-fertilised seeds of tobacco were sown thickly on opposite sides of two additional pots; the plants being left to grow up much crowded. When they were between 13 and 14 inches in height there was no difference between the two sides, nor was there any marked difference when the plants had grown as tall as they could ; for in one pot the tallest crossed plant was 26~ inches in height, and exceeded by 2 inches the tallest self-fertilised plant, whilst in the other pot, the tallest crossed plant was shorter by 3~ inches than the tallest self-fertilised plant, which was 22 inehes in height. As the plants did not grow to their proper height in the above small pots in Table LXXXIV., four crossed and four self-fertilised plants were raised from the same seed, and were planted in pairs on the opposite sides of four very large pots containing rich soil; so that they were not exposed to at all severe mutual competition. When those plants were in flower I neglected to measui:e them, but record in my notes that all four self-fertilised plants exceeded in height the four crossed plants by 2 or 3 inches. We have seen that the flowers on the original or parent-plants which were crossed with pollen from a distinct plant yielded much fewer seeds than those fertilised with their own poll on; and the trial · just given, as well as that in Table LXXXIV., show us clearly |
