OCR Text |
Show 44 IPOJ\HEA PURPUREA. CHAP. II. crossed plants are slightly inferior i~ ?eight and in earliness of flowering to the self-fertihsed. But the I· nf en·o n't y I·n hei'ght is so sn1all ' namely as 100. to 106, that I should have felt very doubtful on this head, had I not cut down all the plants (except those in the crowded pot No. X.) close to the ground and weighed thein. The twenty-seven crossed plants weighed 16~ ounces, and the twe~ty-~even sel~-fertilised plantg 20~ ounces; and this g1ves a ratio of 100 to 124. .r.\.. self-fertilised plant of the same parentage as those in Table XII. had been raised in a separate pot for a distinct purpose ; and it proved partially sterile, the anthers containing very little pollen. Several flowers on this plant were crossed with the little pollen which could be obtained from the other flowers on the same plant; and other flowers were self-fertilised. Fro~ .the seeds thus produced four crossed and four ~elf-fertthsed plants were raised, which were planted In the usual manner on the opposite .sides of two pots. All the~e four crossed plants were inferior in height to theu opponents; they averaged 78 ·18 inche~, whilst the four self-fertilised plants averaged 84 · 8 Inches ; or as 100 to 108.* This case, therefore, confirms the last. Taking all the evidence together, we must conc~ucle that these strictly self-fertilised plants grew a httle taller, were heavier, and generally. flowered before those derived from a cross between two flowers on the same plant. These latter plants thus present a wonderful contrast with those derived from a cross between two distinct individuals. * From one of these self-fertilised pln.nts, spontaneously selffertilised, I gathered twenty-four cap~mles, and they contained on an averaO'e only 3 · 2 seeds per capsule; !:'so that this plant had apparently inherited some of the sterility of its parent. CHAP. II. CROSS WITH A FRESH STOCK. 45 The Effects on the Offspring of a Gross with a distinct or fresh St.ock bel~nging to the same Variety.-From the two foregoing se1?es of experiments we see, firstly, the good effects dunng several successive generations of ~ cross between distinct plants, although these were In some degree inter-related and had been O'rown under nearly the same conditions ; and, secondl;, the absence of all such gooJ effects from a cross between flowers ?n the sa~e plant ; the comparison in both e~ses bei~g made w1th the offspring of flowers fertilised w~th then own pollen. The experiments now to be gi~en show how .powerfully and beneficially plants, whiCh have been 1ntercrossed during many successive generations, having been kept all the time under nearly uniform conditions, are affected by a cross with a~o~her plan_t belonging to the same variety, but to a distinct family or stock, which had grown under different conditions. . Several flowers on the crossed plants of the ninth generation m Table X., were crossed with pollen from another crossed pJant ?f the same lot. The seedlings thus raised formed the tenth mtercrossed generation, and I will call them the "interc1·ossed plants: " Se vera 1 . ot he r fl owers on the same crossed plants of t~e nmth ~eneratwn were fertilised (not having been castrated) With ~ol~en taken from plants of the same variety but belonging to a distinct family, which had been grown in a 'distant garden ~~Colchester, and therefore u~der somewhat different conditions. fe e .capsul~s produced by this cross contained, to my surprise, wer and hgh ter seeds than did the capsules of the in tercrossed E:nts;. but this, I think, must have been accidental. The seedt gs raised from them I will call the " Colchesttr-c1·o8sed." The t:o lots of seeds, after germinating on sand, were planted in . e ~s~al manner on the opposite sides of five pots and the :remamm.o o· seed s, wh e the r or not I.l l a state of ger'm ination ;~re thic~ly sown on the opposite sides of a very large pot: · VI., In Table XIII. In three of the six pots after the young plants had twined a short way up their sticks,' one of the |