Nov. 29,1915 
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 (1913, 
p. 339) >we must refer to the enzym demonstrated by Cooley as ‘ ‘ pectase . 99 
The attempts of Cooley (1914) 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 affinity 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 
(1911) as being less subject 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 ( Prunus besseyi X Sultan, P. triflora) and Wakapa 
(Red June, P. triflora , X DeSota, P. americana , but resembling very 
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. 
