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Show 256 SUMMARY OF MEASUREMENTS. CIIAP. VII. with various surrounding species. The seeds sown at the same time in a garden have generally been Inatured during the same season and in the same place; and in this respect they differ much from. the seeds sown by the hand of nature. Some exotic plants are not frequented by the nati:e insects in their ~ew home, and therefore are not Intercrossed; and tlns appears to be a highly important factor in the individuals acquiring uniformity of constitution. In my experiments the greatest care was take1~ ~hat in each generation all the crossed and self-for!·1~1sed plants should be subjected to the same conchtwns. Not that the conditions were absolutely the same, for the more vigorous individuals will have robbed. the weaker ones of nutriment, and likewise of water when the soil in the pots was becoming dry; and both lots at one end of the pot will have received a little more light than those at the other end. In the successive generations, the plants were subjected to. somew.hat different conditions, for the seasons necessanly vaned, and they were sometimes raised at different periods of the year. But as they were all kept under glass, the~ were exposed to far less abrupt and great cha~ges of te1nperature and moisture than arc plants growing o~t of doors. With respect to the intercrossed plants, th2ll' first parents which were not related, would almost certainly hav'e differed somewhat I. n const1. tutJ.o n.; an d such constitutional peculiarities would be vanol~sly mingled in each succeeding intercrossed generatiOn, being sometimes augmented, but more comm?nly. neutralised in a greater or less degree, and sometimes revived through reversion; just as we know to .be the case with the external characters of crossed spem~s .and varieties. With the plants which vvere sel~-fertihsed during the successive generations, this latter Important CHAP. VII. TABLE C. 257 source of some diversity of constitution will have been wholly eliminated; and the sexual elements produced by the same flower must have been developed under aR nearly the same conditions as it is possible to conceive. In Table C the crossed plants are the offspring of a cross with a fre.:Jh stock, or with a distinct variety; and they were put into competition either with self-fertilised plants, or with intercrossed plants of the sa1ne old stock. By the term fresh stock I mean a non-related plant, the progenitors of which have been raised during so1ne generations in another garden, and have consequently been ~xposed to somewhat different conditions. In the case ·of Nicotiana, IberiE?, the red variety of Primula, the common Pea, and perhaps Anagallis, the plants which were crossed may be ranked as distinct varieties or sub-varieties of the same species; but with Ipomrea, Mimulus, Dianthus, and Petunia, the plants which were .crossed differed exclusively in the tint of their flowers; and as a large proportion of the plants raised from the same lot of purchased seeds thus varied, the differences ·may be estimated as merely individual. Having made these preliminary remarks, we will now consider in detail the several cases given in Table C, and they are well worthy of full consideration. (1.) Ipomcea purpurea.-Plants growing in the same pots, and subjected in each generation to the same conditions were intercrossecl for nine consecutive ' generations. These intercrossecl plants thus became in the later generations more or less closely inter-related. Flowers on the plants of the ninth intercrossecl generation were fertilised with pollen taken fron1 a fresh stock, and seedlings thus raised. Other flowers on the same intercrossed plants were fertilised with pollen from another intercrossed plant, producing seedlings of the tenth intercrossecf generation. These two sets of s |