W. A. (linON. 



KEVjaol'Mli.M (IK IIISKASK IIKSISTA.M VAKIKTIES dl' l'I.A.NÏS. 



THE DEVELOPMENT OF DISEASE RESISTANT VARIETIES OF PLANTS' 

 By W. A. ORTON 



l'atliolotlisl, [lui. MU (.1 l'huU liulusljy. 



V. S. De|i.ni-tmoiit ol' A;; 



WasIiiuRlon D. C. 



Tlic problenis connccteil willi Ihc sliuly of Iinmunity aiid Ihc di'\i'l(i|)im'nl 

 of new varielics ol' plants resislanl to diseases inspire the investigalor wlio works 

 in this borderlanti between Pathology and Gene- 

 tics wilh a tliree lold inleresl, Ijecause of the 

 opporliinilies Uial are presenled lo promole the oiie 

 science Ihru contributions lo our knowledge ni' 

 parasilisin, and Ihe otiier by adding data on varia- 

 tion and heredity, wiiile al the same lime he pre 

 sents to agriculture new means for the more cfli- 

 cient control of disease. 



l'he nature of the subject requires also liial 

 one sliould acquire the triple viewpoinl of liie pa- 

 tholog'ist, of Ihe lireeder and of the farmer, and 

 bring to his task the equipment of ail tliree. 



To Ireat Disease Résistance in plants exhaus- 

 lively IVoin ail lliree slandpoinls, would, however, 

 far exceed the limitations of this paper, and would 

 tax unnecessarily Ihe patience of an audience inle 

 rested primaiily in (jlenetics. \\'e désire, never 



. . M (lllln\ 



theless, todelay our discussion ofdisease-rosistance 



as an inheritable character, while \ve defîne briefly our conceptions of disease, 

 of the nature and degrecs of parasitism and our viewpoinlof immunily, in order 

 to présent to the sludent of Genetics somelhing of the viewpoinl of the palho- 

 logist on thèse questions-. 



We may dcline disease as any deparlure IVom the normal dcvelopmcnl and 

 metabolism of a plant. Two great groups of diseases may convcnienlly bc esla- 

 blished — Ihc parasilic and the non parasitic. — In the latler are included the 

 physiological ellects of deficiencies or excesses of nutriment, the inlUn-nce of 

 unfa\orable soilsand wealher, of unaccustomed climatesand th(> like. Hcre the 

 sludent of genclics may find rich material if he will study the adaptation of 

 planls lo their cnvironmenl, the effect of food supply on variation, the résistance 

 to drought, tu l'rosl and to beat, wilh respect to inheritance. 



We shall dwell later on the influence thaï the physiological condition of a 

 plani may hâve on ils résistance or susceplibility to disease, but wilh this 

 exception shall not deal in this paper wilh résistance to non parasilic diseases. 



Parcoiili^^m frnm Ihc Evolution ]'i('ir/ioiiil . — Parasitism is a method of 

 nuti'ilion thaï lias liccn developed by cei'tain oi'ganisms, whereby Ihi'y livi^ in 



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Ml' ù la ti'oisièniL' sraiiir île la Coiirùrciicc. 

 Iiavelopment ol'l''ann (IniiisRcsisIniil lo l)i: 



0, Yr„rh(,nl.-. U. S. tlri„irlii 



