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Show PISUM SATIVUM. CHAP. v. 160 . . 1 d place in a shrubbery. Hero lots of seeds in poor smlln a s ~a ~ the self-fertilised for a long , aain the self-fertilised plan~s hr~ ht those from the previously at1o·m e exceeded consl· a erab .l y 1n mg bab1y be attribute cl ' l·n tho crossed plants; an d th1s em atyo pthroes e seeds havm· g gcrmm· a t oc l present as in the last casf: the crossed plants; hut at. tho rather sooner than those ro~ f the solf-fcrtilisocl plants from clo. e of tho season the tall~s lo hilst the tallest of the ,'elf-d l t was 30 Inc 1es, w . the crosse pan s . Tsed was 29* inches in hmg1.1t. . fertilised from the self-fertll .· we see that plantR donved From the va.rw. us facts now. t'g ivenf the sweet-poa . h d'A' two var1e 1es o ' wblC luor J from a cross between 1 ""' of their flowers, exceoct t in the co oul. . . in no respect excep ffi . from elf-fort1hsed plants, considerably in height the ~ spn~;ations The eros. cd plants both in the first and sec?n 't ge_n heio·ht. and vigour to their also transmit their. supenorl y In b . self-fertilised offsprmg. PISUM SATIVUM. . f ctl fertile when its flowers are pro- The common p. e'atl S fp e. r see ctsy. I ascer tai·ned this. with two or tected from the Vl~l ~ o In .d D Qale with another. But the three different vanetles, as dl r. b f ti.ll. ation. Mr. Farrer . . dapted for cross- er · ' . flower::; are hkewise. a . 1 . " The open blossom dis-specifies* the following pmnts, ~·arne y d convenient position for playing itself in th~ most att~~lc lV~ ::e wings formiug an alig~1tinsects; the conspiCuous vexl urn' ·nas to the keel, by whiCh ing place; the attachment ?f th~ Wl t press down the ]utter; any bod~ pressing on t?e former ~:~affording by moans of its the stam1nal tube enclos~ng nectar, n each side of its base an Partially free stamen with apertures o t . the moist and . t k'ng the nee ar, open passage to an .lnsec se~ 1. will bo swept out of the apex sticky pollen p~aced JUSt wh~re. 1: t. the stiff elastic style so of the keel agmnst the enten~g Inse~i~d to the keel it will be placed that un a pressure bemg app . . the style placed pushed upwards out of the keel; the] ~~r:h~;c is space for the On that side of the style only on w 11C 't out. and the Pollen aud in such a du· ec tw' n as to sw. oop . 1 t _'a ll these stigma' so placed as to meet an en te-nnO' 1nsec ,, b echaniRm, if we become correlated parts of one ela bora tc m * 'Nature,' Oct. 10, 1872, p. 479. H. Muller gives an olubomtc d cscn.p t 'L O n of the flowers, fruchtung,' &c. P· 247· 'Be· CHAP. v. PI SUM SA rriVUM. 161 suppose that the fertilisation of these flowers is effected by the carriage of pollen from one to the other." Notwithstanding these manifest provisions for cross-fertilisation, varieties which have been cultivated for very many successive generations in close proximity, although flowering at the same time, remain pure. I have elsewhere* given evidence on this head, and if required could give more. There can hardly be a doubt that some of Knight's varieties, which were originally produced by an artificial cross and were very vigorous, lasted for at least sixty years, and during all these years were self-fertilised; for had it been otherwise, they would not have kept true, as the sevt-ral varieties are generally grown near together. Most of the varieties, how. ever, endure for a shorter period; and this may be in part doe to their weakness of constitution frmn long-continued selffertilisation. It is remarkable, considering that the flowers secrete much nectar and afford much pollen, how seldom they are visited by insects either in England or, as II. Mittler remarks, in North Germany. I have observed the flowers for the last thirty years, and in all this time have .only thrice seen bees of the proper kind at work (one of them being Bomb us m~tscorum ), such as were sufficiently powerful to depress the keel, so as to get the undersides of their bodies dusted with pollen. These bees visited several flowers, and could hardly have failed to cross-fertilise them. Hive-bees and other small kinds sometimes collect pollen from old and already fertilised flowers, but this is of no account. The rarity of the visits of efficient bees to this exotic plant is, I believe, the chief cause of the varieties so seldom intcrcrossing. That a cross does occasionally take place, as might be expected from what has just been stated, is certain, from the recorded cases of the direct action of the pollen of one variety on the seed-coats of another. t The late Mr. 1\fasters, who particularly attended to the raising of new varieties of peas, was convinced that some of them had originated from aecidental crosses. But as such _crosses are rare, the old varieties would not often be thus doteriorated, more especially as plants departing from the proper type are generally rejected by those who collect seed for sale. There is another cause which probably tends to render cross-fertilisation rare, * ' Variation of Animals and Plants under Dome~tication ' ch a p. 1. x. 2nd edit. vol. i. p. 3:1:8. ' t 'Var. under Domestication,' chap. xi. 2nd edit. vol. i. p. -:1:28. M |
