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Show 350 SELF-FERTILE VARIETIES. CBAJ>, IX~ thoRe which were crossed; and tho seedlings raised from these self-fertilised seeds exeeeded in h~ight those raised fro1n the crossed seeds to an .extraonhnary d egree. In the second and. third generation , althoug. h the self-fertilised plants did not exceed ~he crossed 1n height, yet their self-fertilised flowers y1elded on two occasions considerably 1nore seeds than th? crosse(1 flowers, even than those which were crossed wtth pollen fro In a distinct stock or variety. Lastly, as certain individual plants of ~eseda oclorata and lutea are inco1nparably Inore self-fertile than other individuals the forn1er n1ight be included unuer the present he~ding of the ap~eara~ce of new and highly self-fertile varieties. But In this case we should have to look at these two species as nonnally self-sterile; and this, judging by n1y experience, appears to bo the correct view. We may therefore conclude from the facts no·w given, that varieties sometimes arise which when self~fertilised possess an increased po·we~ of produeing :seeds and of growing to a greater height, than tho In~ercrossed or self-f rtilised plants f the corresponchng generation-all the plants being of course su~jected to the saine conditions. 'fhe appearance of such varieties is interesting, as it bears on the existence under nature of plants which regularly fertilise th~mselves, such as Ophrys apifera and a few other orchids, or as Leersia oryzoides, which produces an abundance of cleistogene flowers, but most rarely flowers capable of cross-fertilisation. Some observations made on other plants lead me to suspect that self-fertilisation is in so~lO r~spects beneficial; although the benefit thus denved IS a~ a rule very small compared with that from a cross with a distinct plant. Thus we have seen in the last chapter CHAP. TX. SELF-FERTILE VARIETIES. 351 that seedlings of Iponlooa and J\Iinrnlus raised f fl f . 1 . d . c rom owers erti tse , w1th their own pollen h' h . h . . , W lC IS t e stnctest posstble fonn of self-fertilis·1t1'on we · • · 0 . . • " , re supenor In .hete,ht, wetght, and In early flowering to the seedlino·s ratsecl from flowers crossed with pollen frotn other flowe~s on the same plant; and this superiority apparently was t?o strong!~ ~arke<.l to bo accidental. Again, the cultt va.ted vanettes of the coin In on pea are highly selffertile, a.l though they have bee. n self-ferti'l1'sed 11! 0r mttny g.enerat~~ns; and they exceeded in height seedlings from a cross between two 11lants bolono·in<Y to th . . r o <:") e smne va~·~ety In the ratio of 115 to 100; but then only four paus o~ _rlants we:·e mec1sured and compared. The self-fert.i lity of Pnm~da veris inc1·eased aft er severa1 generations of illegiti1nate fertilisation, which is a process closely analogous to self-fertilisation, but only as long as the 1:l~n ts were cultivated under the same favourable conditions. I have also elsewhere sho * tha~ ~i th P r~1nula veris and sinens~s, eq ual-st~~d varrettes occasionally appear which possess the sexual organs of the two forms combined in the sa1ne flower. Consequently the! fertilise themselves in a Iegiti1nate man~er and are highly self-fertile; but the remarkable fact Is that they are rather more fertile than ordinary plants ,of the ~ar;ne species legiti1nately fertilised by pollen from a distinct inclivi~ual. Fonnerly it appeared t~ me P.robable, that the Increased fertility of these di~orphic plants Inight be accounted for by the stigma lying so close to the anthers that it was i1npregnatecl at the most. fav?urable age and time of the clay; but this ~xpla~ation Is not applicable to the above given cases, In ~hich the flowers were artificially fertili~ed with then own pollen. * 'Journal Linn. Soc. Dot.' vol. x. 1867, pp. 417, 419. |