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Show 34 INHERITANCE. CHAP. XIII. h . cters which would be l d enlargement of cer t am· parts '-. c adr a t ·uo·aling wr' th ot l1 er succu encv an '· . oor sml an s I bb 1 tl surely lo;t by plants growing m a. p 'ld on so enormous a sea. e as 1e lants. No cultivated plant ~as run w~ Every botanist who has seen p < l (Cynam cll7·dnnwlus) m La Pla a. h 's back has been struck care oon b d high as a orse • ' t t · t it growing there, in vast e s, as . it differs in a.ny impor a.n . POl? 'th its peculia.r a.ppeamnce ; but whe~her. . d not to be prickly like rts wf.r the cultivated Spam.s ,J l £0 1· m which IS sar "" lit . ·ane·m ' . . • f. m the wild lhec or:. • rom d t r wllether rt differs ro America.n clescon an ' o . l I clo not know. specw. s , which is saicl not to be Rocm' if . Cross in the case o nz t derwed from a ' . Reversion to vaarac ers . Wh an individual havmg Sub~varieties, R aces, an d . 81r.1 eczes· - . .e 'nt h another of the same . bl hanty umtes WI . f some recogmza e pecu 1 . ··t in question, It o ten t h · g the pecu Iall Y sub-variety, no avm . terval of several gene- . h d dants after an m 1 reappears m t e escen t' d or heard from old peop e rations. E very one must hav.e n. o . we . p' pearance or menta1 d'I S- 1 1 resem blmo m a · of children c ose Y 0 1 character as expressiOn, position, or in so small and comp ex a more distant collateral h · ndparents or some . Jo one .o f t eVu· gra ' 1' f structure and diseases, any anoma Ies o h relatiOn. ery m . in the last chapter, ave of which instances have been give~ t and have reappeared . f: ']y from one paren ' · come mto a ami . . two or three generatiOns. in the progeny after passmg over . cated to me on good . has been commum . h The followmg case . be full trusted: a pointer-bite authority, and may, I _behe:e, ·ey marked with blue and d Pp1es · 1our wei produce seven pu ' 1 . 'th pointers that she was · 1 · nusual a co om WI d white, whw 1 IS so u . l f the grevhounds, an h 1 red false Wit 1 one o J thought to . ave p a) d . but the gamekeeper was per-the whole htter was cond~.m~: ' Two years afterwards a friend mitted to save one as a CUll~~l x· . and declared that he was the of the own~r saw th~ yo.un_o hog, ho the only blue and white image of his old pomtei-bitc app ' This led to d t which he had ever seen. pointer of pure escen . d th t he was the great-great- . · nd it was prove a close mqmry, a 1. t the common expres-randson of Sappho ; so that, accorc I_ng _o . E . it can g_ h had only 1-16th of her blood m his vems. ere 'th slwnd,l eb doubted that a character derived from a cross w.J 1ar . yd ' e' dual of the same \ariety reappeare d a ft ei· r1aSSJOP' an m IVI o over three generations. . t . the ' British and Foreign 1\icd.· 15 1\ir. Scllgwick gives many ms ances m Chi.rurg. Review,' April and July, 1863, pp. 448, 188. CrrAP. XIII. REVERSION. 35 vVhen two distinct races are crossed, it is notorious that the tendency in the offspring to revert to one or both parentforms is strong, and endures for many generations. I have myself seen the clearest evidence of this in crossed pigeons aud with various plants. Mr. Sidney 16 states that, in a litter of Essex pigs, two young ones appeared which were the image of the Berkshire boar that had been used twenty-eight years before in giving size and constitution to the breed. I observed in the farm yard at Betley Hall some fowls showing a strong likeness to the Malay breed, and was told by Mr. Tollet that he had forty years before crossed his birds with Malays; and that, though he had at first attempted to get rid of this strain, he bad subsequently given up the attempt in despair, as the Malay character would reappear. 'rhis strong tendency in crossed breeds to revert has given rise to endless discussions in how many generations after a single cross, either with a distinct breed or merely with an inferior animal, the breed may be considered as pure, aud free from all danger of reversion. No one supposes that less than three generations suffices, and most breeders think that six, seven, or eight are necessary, and some go to still greater lengths.17 But neither in the case of a breed which has been contaminated by a single cross, nor when, in the attempt to form an intermediate breed, half-bred animals have been matched together during many generations, can any rule be laid down how soon the tendency to reversion will be obliterated. It depends on the difference in the strength or prepotency of·transmission in the two parent-forms, on their actual amount of difference, and on the nature of the conditions of life to which the crossed offspring are exposed. But we must be careful not to confound these cases of reversion to characters gained from a cross, with those given under the first class, in which characters originally common to bot!~ parents, but lost at some former period, reappear; for such characters may recur after an almost indefinite number of generations. 16 In his edit. of 'Youatt on tbe Pig,' 1860, p. 27. 1 i Dr. P. Lucas, 'Hered. Nat.,' tom. ii pp. 314, 892: see a good practical article on this subject in ' Gard. ChTonicle,' 1856, p. 620. I could add a vast number of references, but they would be superfluous. D 2 |