Nov. 15,1925 Crown-gall Studies of Resistant Stocks for Prunus 
963 
Four different seedlings of the sand cherry, P. pumila , have been 
used in the inoculation tests, and it seems to be somewhat more 
resistant than the variety of P. besseyi , known as the Rocky Mountain 
Dwarf. This stock was purchased from an eastern nursery, and it 
is not known whether the inoculations were made on seedlings or on 
stock grown from cuttings from a single source. P. pumila grows 
readily from cuttings planted in the spring, and the same is probably 
also true of P. besseyi. The black sloe (P. umbellata) is rather 
promising. It produces a good-sized tree and does not sucker badly. 
Amygdalus tangutica may be valuable as a dwarf peach and almond 
stock, though it is said to sucker freely, which is an objection. P. 
mume is the most promising species, and will be considered later. 
Amygdalus mira (the smooth-pit peach) and A. persica potanini are 
promising. They seem to be vigorous growers and should be further 
tested. 
The results are given in Tables I to III can be summarized by 
arranging the species of Amygdalus and Prunus in the following 
groups: 
(1) Amygdalus: mira , tangutica,persica, communis; 3 to 88 per cent. 
(2) Evergreen species (Laurocerasus): caroliniana, ilicifolia, lyoni; 0 to 3 per 
cent of infection. 
(3) Sand plums: pumila, besseyi ; 0.2 to 10 per cent. 
(4) Domestica: 17 varieties tested (Table II); 3 to 95 per cent. 
(5) Damson ( insititia ): St. Julian, Shropshire; 10 to 87 per cent. 
(6) Subdesert species: andersoni fasciculata , fremonti, microphylla, minutifolia ; 
20 to 50 per cent. 
(7) Sloelike plums: alleghaniensis, spinosa, umbellata (S. P. I. 38974 
and seedlings of umbellata (S. P. I. 38974); 0.6 to 88 per cent. 
(8) Chickasaw plum: angustifolia, angustifolia watsoni; 24 to 37 per cent. 
(9) Myrobalan plum (cerasifera) : seedlings, var. divaricata, and seedlings of 
var. pissardi ; 75 to 90 per cent. 
(10) Apricot ( armeniaca ): Royal, Royal seedlings, Blenheim, Tilton, etc., and 
var. mandshurica ; 8.3 to 95 per cent. 
(11) Japanese apricot {mume): 46 seedlings (Table V); 1.5 to 13 per cent. 
The Black Sloe (Prunus umbellata) 
This species is one of the most promising of the native forms of 
Prunus for use as a rootstock for the stone fruits. It has been used for 
rootstocks in Florida. In California, under the climatic conditions 
of Riverside, it makes, the first season, a stocky growth of 3 to 4.5 
feet in height. Tests are under way to determine its adaptability 
for the different varieties of the stone fruits. The results of the 
artificial inoculations as listed in Table I showed a single tree of 
P. umbellata (S. P. I. 38974) as less susceptible than P. umbellata 
injucunda (.P . mitis Beadle), but further inoculation tests of the former 
on more rapidly growing wood are necessary before its crown-gall 
resistance can be considered as established. 
In Table IV are given the tabulated results of inoculation of seedlings 
of Prunus umbellata (S. P. I. 38974). Control inoculations were 
made on seedlings of Indian Cling peach. Eighty puncture inocu¬ 
lations gave 53 galls or 66 per cent infection, which result agrees 
very closely with 64.9 per cent given for this form of P. persica in 
Table I. 
