•2 G 8 



CAUSES OF VARIABILITY. 



Chap. XXII 



variation the action cannot have been throng the reproduce 



ve 



syst in. 



ight< ntl 



1 



stem takes in cansiii 



ter that even slight 



cans 



- 



a 



variability, we have seen h th* 

 chan.L ■ in the -nditions of life '. 

 gi ater »r k ? cl gTee of sterility. Hence it s ms u t i: obaMe that 



enerated through a system so t siio ■ ff. ■: . 1 t 

 I"-: eted. r r . . jiiLI fail to inherit, <>r inj rit in excess. . - . 



pr :r to their parents. Wo know that cert' a groti] ^ 



P - ^ 



but with exceptions in each group, have tt r rep] ductive s; .s i 



more ei ily affec^ d by changed conditions than - er gr os: for in- 

 ^ance, carnivorous icrds more readily than carnivorous momioo^, i 

 1 iTots more readily than ok ms ; and this fact harmonizes ^i th 

 apparently capricious manner and d> ■ in which 

 animals and plants vary under domestic tion. 



grout 



Kblreuter 47 was struck with the parallelism ,tw n the ex siye 

 variability <«f hybrids when cr<-.- 1 and recrossed 



m various ways 



t hybrids Oaring their reproductive p< vers i ,r L f.-cted, 



and the variability of an : atly cultivated plants. Max VO .ur ; 

 gone one step farther, and shows that with many ■ -i our hi. ■ultiva- I 

 ] ints, such as the hyacinth, tulip, auricula, snapdragon, potat:-. 

 &e., which there is no reason to Olf w :i ave been h} ridO [. a . n th. 

 contain many irr ular pollen-grains, in th same' state as in hybrids 

 He finds also in certain wild forms, the same coin • lenoe I -n t >wt, 



idcev 



si 



species, the 



pollen is sound. It is also notorious that many cultivated plant.. - 

 as the banana, pine-apple, breadfruit, and others previouslv men ned. 



so 



qui sterile ; and when they do yield st :1, the seedling, Oddn.Oroin ti 



races which exist, must 1 variable in a; 



large nurabei 



extreme deor 3. 



ted 



m 



S( I 



me rdatiun between 



the state of the reproductive organs and a tendency to variabilis: but we 

 must i .t conclude that the relation is strict. Although nianv of ur 

 high! cultivated plant, may have their i lien in a deteriora 1 , ndition, 

 yet, a. we have previously ^en, they yield mor- 1, and our anciently 

 mesticated animals are more prolific, than the a-respondm- s] s in 

 a -feature. Tb peacock is aim t the onlv bird whielTis 1 ieved 



to be less fertile under domestication than in its native state, and it has 

 varied m a remarkably small o! ,ree. From the, moderations it would 



lif 



bility, or to Loth; and not that sterilitv induces 



■ili 



th 



On the whole 

 a' reproduction would 



f ~ ~™ * " ^ --"«■=« aucLuiig me organs ot reproduetioi 



hk em . affect their product -tb avis, the Oaring thus general I. 



47 • DritteFoitsetzung, , &c.,17 Oks.85. 



'Die 



Bastardbefruchtung,' 



1865, s. 92 : see also the Rev. M. J. 



Berkeley on tl same su . in 

 'Journal of Royal Horu Soe.,' 1866 

 p. >0. 





