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Show 464 GENERAL RESULTS. CIIAP. XII. sp C·ie S 0 f plants are crossed '· they produce with the rares t excep tI·o ns .1!' 'ewer seeds t•h an • the normal • number. This unproductiveness varies In different species up to s t en'l I't y so co mplete that not even an empty capsule · .!' . d. and all experimentalists have found that IS 10rme , · · h' h h it is In uch influenced by the conch t1ons to w Ic t e crosse d spe CI.es are subJ. ected. The pollen of each · ~ spec1· es I·S str·ongly prepotent over that o.f any other speci·e s, so that if a plant's own . pollen Is placed on the s tI. gma some time after foreign poll. en h·a s be,,en 1 . appl I.e d to I.t ? any effect from the latter 1s quito ou l-t erat, ed . It I·s ca. lso notorious that not only the parent speci·e s, but the hybrids raised from . then1 aro. more or less sterile ; and that their pollen IS often In ~ .more or less aborted condition. The dogr~e of stenhty of van.· ou s hybrids does not always stn. c.t ly cho rrespondt with the legr e of difficulty in uniting . t o. paren forms. When hybrids are capable of bre .ding 2nter se, their descendants are more or less stenle, and . they often become still more steril in the later generat1~ns; but then close interbreeding has hitherto been practised in all such cases. The more sterile hybrids are someti1nes much dwarfed in stature, and have a feeble co~stitution. Other facts could be given, but these will suffice for us. Naturalists formerly att~ibute~ all these results to the difference between species bmn$' f~ndaf mentally distinct from that between the :anetles o the same species ; and this is still the verdict of some naturalists. . . · d The results of nly experiments in self-fe:ti~Ising an cross-fertilising the individuals or the v~neties of .th~ same species, are strikingly analogous :Vlth tho:~ 0~~ts given though in a reversed manner. With them J . 1~ of sr)~Ci s flowers fertilised with their own pollen Yf1et. fewer, someti. mes much fewer see d s, tha n those er l· CHAl'. XII. GENEHAL RESULTS. 465 lised with po~l?n from another inrlividual or variety. Some self-fertlhsod flowers are absolutely sterile. but the degr~e. of their sterility is largely clotonnin~d by the cond1t1ons to which the parent plants have be n exposed, as was well oxmnplifiod in the case of Esehscholtzia and Abutilon. Tho effects of pollen fro1n the same plant are obliterated by the prepotent influence of pollen from another inJivi<lual or variety, although the latter n1ay have boeu placed on the stio-1na some hours afterwards. ~rhe offspring from sel~fcrtilised flowers are themselves more or .less sterile, sometimes highly sterile, and their pollen is so1netimos in an imperfect condition; but I have not mot with anv case of co1nplete sterility in self-fertilised seedlings,~ as is so common with hybr~ds. The degree of their sterility does not correspond With that of the parent-plants when first self-fertilised. The offspring of self-fertilised plants suffer in stature, weight, and constitutional vigour more frequently and in a greater degree than do the hybrid offspl:ing of tho greater number of crossed species. Decreased height is trans1nitted to the next generation, but I did not ascertain whether this applies to decreased fertility. I have elsewhere shown* that by uniting in various ways dimorphic or trimorphic heterostyled plants, which belong to the same undoubted species, we get another series of results exactly parallel with those from crossing distinct species. Plants illegitimately fertilised with pollen from a distinct plant belonging to the same fonn, yield fewer, often much fewer seeds, than they do when legitimately fertilised with pollen fro1n a plant belonging to a distinct form. They soinotimes yield no seed, not even an empty capsule, ljko * ' J om·nnl Linn. Soc. Bot.' vol. x. 1867, p. 303. 2 II |