Nov. 29, I9I5 Varietal Resistance of Plums to Brown-Rot 369 



here termed pectase was obtained from malt-extract by Bourquelot and 

 Herissey, who called it pectinase; according to the general principle of 

 naming enzymes after the substrate, this should be altered to pectase." 

 In a subsequent paragraph he states that " By the term pectinase should 

 be indicated the enzyme which coagulates dissolved pectin substances, 

 e. g., in fruit juices, in the presence of lime to gelatinous calcium salts of 

 the feebly acid pectinic acids." If we follow the definition of a pectinase 

 given by Jones and the classification given by Haas and Hill (191 3, 

 p. 339), we must refer to the enzym demonstrated by Cooley as "pectase." 

 The attempts of Cooley (191 4) to isolate a middle-lamella-splitting 

 enzym from rotted fruit gave negative results. In certain artificial 

 media a cellulose-dissolving enzym was produced, but its action on 

 cellulose isolated from plums was very slight. From direct observations 

 on the fungus in free-hand sections of fruit he concluded that " the fungus 

 does not show any particular afianity for the middle-lamella, but pene- 

 trates and permeates with equal avidity any part of the host tissue." 

 He could find no relationship to exist between varying acid content of 

 plums at different periods of development and increased susceptibility 

 of ripe over green fruits. 



EXPERIMENTAL MATERIAL 



The organism used in this work was isolated when needed from rotting 

 plums, as it seemed better to use only strains which had been growing 

 under normal conditions rather than to risk a decrease in virulence of 

 infection due to growing a single strain on artificial media. 



The plums used consisted for the most part of hybrids produced at the 

 Minnesota Fruit-Breeding Station at Excelsior. Those referred to in 

 the text as "B X W" are hybrids of Burbank {P. triflora), the female 

 parent, with Wolf (P. americana mollis). The A X W crosses are Abund- 

 ance (P. triflora) X Wolf. The Burbank is a medium thick-skinned 

 variety which becomes soft when ripe and is rather susceptible to the 

 brown-rot. Wolf has a thick, tough skin and is not affected to any great 

 extent by the rot in the field. Abundance is reported by Hedrick 

 (191 1) as being less isubject to attacks of the brown-rot than Burbank. 

 The crosses B X W15 and A X W18 are both characterized by being very 

 firm when ripe, and are both nearly immune to brown-rot in the field. 

 The other hybrids of these two series vary in firmness and resistance. 



Etopa and Sapa {Pruntis besseyi X Sultan, P. triflora) and \A''akapa 

 (Red June, P. triflora, X DeSota, P. americana, but resembling ver)?- 

 closely a sand-cherry hybrid) are products of the South Dakota Experi- 

 ment Station. They are thin-skinned varieties and are susceptible to 

 rot. The sand cherry (P. besseyi) is a small fruit which becomes soft on 

 ripening. It has very astringent flesh and is susceptible to brown-rot. 



