'^■>i IV CdMKIlKNCK l\Ti:ll\AT|((\\|.K DK l.K.NKTUM i;. 



Il .llliicks lioll) llic l'oiiiinoii r|)hiliii ( 

 Island <-ol(,()ll i< i(}<:>il//iiinii hinhailriiSir) 



Tliere is vory lilllr \;iricl,il icsisliuice, 

 (han lialf disiNiscd. AI i;ir<' inlorvals I 

 vidual plaids whii li icmaiii licailliy. 

 aclually rcsislani aiul llial oliicrs lia\i 

 oulffrown llic iiivadint; l'iiiii 



cases iiidii \\i 



lii 



\\:i 



iilhf 



dIIuii ((inxsi/])iinii hh-Hiilum) ami llic Sea 

 llii' l'ornier somowhat moro sevcrcdy. 

 lie licsl Ivinds in ||ii< respect are more 

 icrr occiir in niiirji ird'ected (ields indi- 

 II is Urjicxcd lliat some of lliese are 

 .iiridcnlally eseaped iiifeclion. or liavc 

 Il i-- diriiiidl lo dislinji'iiisli helwccn tlicsc 

 i.M.ilciy in a llioroly iiirecled field. wiirn w c 

 liiid Uial some, usuallyonly a small 

 percentage, of our seleclions, can 

 Iransmil llieir résistance lo liieir 

 ollspriiig. Tlie cause of Ihis rcsis- 

 lance is net fully established, I)ut 

 lliere is évidence to indicate Ihat il 

 is a physiological rallier llian a 

 morphological qiialily. No diire- 

 rences liave been found between 

 immune and susceptible planls in 

 Ihe slruclure of rools or vessels 

 (llie paris altacked) or in form of 

 leaf, habit of growlh or color of 

 foliage. Neilher are there obser- 

 valile dilTerences in lime of germi- 

 nation, rate of dcveloiiMienl or 

 pcriod of malurily. 



Tiie résistance is spécifie. 

 Varielies wliich resisl one disease 

 maybe susceptible loanolher — e. g., Cenlerville Sea Island Collon resislsboth 

 will and baclerial bliglil [Baclcrium malvacearum) wliilelhc Riversis wilt-resis- 

 lanl. but susceptible to l)acterial bliglil. Finaliy, analogy wilh diseases of 

 mankind and animais leads us to search for pliysiologieal rallier than structural 

 qualilies. 



The résistance behaves as an inheritaljle (diaracter. By discarding ail llie 

 seleclions which show indication of susceptibility lo wilt, and applying lo Uie 

 remainder Ihe melhods of line breeding, il lias been possible le develop well 

 fixed varielies possessing almosl complète disease résistance. Tins résistance 

 is augmenled rallier than diniinished during succeeding years unless the sélec- 

 tion is disconlinued, in which case several causes lend toward détérioration. 



Thèse are, in the orderof Iheir praclical importance, (f) mixture wilh seed of 

 non-resislant sorts al the public gins ; \i) cross pollination wilh non-resislant 

 collon in neighboring fields, thru the agency of insccts; Ti) variation or rever- 

 sion \\ilhin Ihe variely, due, perhaps to Ihe influence of crosses in previous 

 générations. 



The working metliods followed in our breeding of will-resislant collon are 

 in essential principlcs similar lo llios(^ of IjriMNlers working wilh ollier |ilants. 

 Disease résistance is madc the lirsl rcipiiremeiil . The earlicr work ' was cnlircly 



1. ORroN{\V.-.\.;. TlicWill ItiM^snil' Cclhm .nul Us Cniilinj. 1;mI.'27. Wr. IVc/. f/iys.niid l'nlli.. liMIO. 

 Iiiiii. On Ihe lii-eeilin^ ol' Disease iiesisNiiil V.iiielies. l'nu-. liiln-nalional Cniifnrinr un j'Iniil 

 Hirediiig nnd llifbiiiihntirDi. \'MH. pp. 41-ô"i. 



l'Ion, iljnslraling' VAeu ly|ie, lin 

 parent of llie liybrid. 

 5. — Pastèque, lype " Eden '', plante mère ilr riijliridi- 



