W. A. (lUTON. ~ THE Dl'VKLOl'MI-.M (II- DISEASE ItESISTA.NT VAUIETIES OF PLANTS. 201 



Ail thèse Avere rejected antl the sclcclion of individuals conlinued fiA'e years 

 loiii^cr. The resull is a melon Avich lias liecn naiiied Ihe Conqueror, oC greal 

 uniformily and diseasc-resistance, with a thin lough rind, Avhich enables il lo 

 endure long raihvay shipmenls. The fruits relain Iheir quality unnsually long 

 afler malurily and are nol quickly sunbiirned. The flesh is so juicy thaï Ihe 

 melons are heavier Ihan the Eden melons of fhe same size. The qualily and 

 flavor are good, Ihougli nol equal to the fincst. Thèse characters hâve becn 

 preserA'ed as far from the place of origin as eastern lowa, 740 miles, but in 

 Oregon, on Ihe Pacific Coast the résistance has not been maintaincd. W'e now 

 belieAe thaï changes of climale influence the inherilance and thaï il will lie 

 necessary lo devclop locally adapled varieties This highiy importanl phase of 

 heredily sludies has nol of laie received the attention il deserves. Such work 

 has becn undertaken for Xorlh-Carolina, where in coopération Avith the North 

 C.nrolina Experiment Station Ave are seeking to producc a variely bélier adapled 

 lo Iheir conditions and niai'kels llian the ( ",oni|ueror. 



DlSEASE RESISTANCE l.\ THE l'OTATO. 



During the past six years much has lieeii donc in the United States on the 

 disease résistance of Ihe potato. We hâve to deal w ilh Late Blighl (Plii/lnpli- 

 t/iora iiif'estnns), Avith aaIU {Fusarhim oxyspor/nii). willi early blighl (AUfvnarin 

 solani) and Avith scab (Oospora scabies). 



The most significant results hâve been oblaincd liy Prof. L.-R. Joncs' wlio 

 has shown Ihru cultures of Phijlopluhoia on raw Idocks of potato, thaï Iherc 

 is much dilference in varietal susceptibility, and tliat Ihis may be measured by 

 a laboratory lest, according to the aniounl of growlh on the uncooked inocu- 

 lated surface afler a fixed lime. This is interpreted to mean thaï the résistance 

 is a physiological reaction of the living protoplasm. Certainly il is nol due lo 

 a protective epidcrmis. Résistance of foliage lo Pliytophthora may, however, 

 as pointed oui by Sluart- be associated Avilh a morphological character, i. e. 

 a ihick, firm hairy leaf, of small size, with an opcn babil of growlh, and less 

 favorable for the germination of spores. 



( iENERAI. CONCLUSIONS. 



Taken together, and in relation to the results secured in France, with 

 résistant vines, Ihe outlook for furiher application of the principle of breeding 

 disease résistance is hopeful. Too much must nol be expected. It is more 

 Ihan a mère Mendelian recombination to be effected in Ihree or four years. The 

 factors influencing success are numerous, for example, Ihe nature of the para- 

 site, the genetic character of Ihe host, whcther a basis for breeding is available, 

 Avhelher market quality can be had. In highiy bred crops thèse attainmenis 

 arc correspondingly difficult. Disease résistance should, nevertheless, be 

 aimed for in ail breeding. 



1. .lo.sEs, fiiiiBiNGs and Litmaw Investigations or tlie Potatir Fungus. Pliytophlliora infoslan*. limniii 

 of Plant Imluslnj. Bull, n" '215; 1912. 



2. SinAiiT (\Vm.). Disease ficsistance of Polaloes. IV. A'j. K.rj). SUt. Uni., ii" l'Ji. 



