516 
Journal of Agricultural Research voi. xxix, no. 10 
horticulturists recognize, however, the 
importance of the rootstock in its 
relation to soil conditions, to disease 
resistance, to uniformity of growth, 
and to the manner of union with the 
scion. In breeding for disease resist¬ 
ance it frequently happens that the 
resistance sought for resides in & dis¬ 
tinct species. Such a species may or 
may not graft readily with the com¬ 
mercial type which it is desired to 
grow. It might be possible to unite 
the qualities of disease resistance and a 
possibility of grafting by hybridization. 
Such a hybrid would of course be 
heterozygous and would segregate in 
succeeding generations. In order to 
produce a desirable type for the propa¬ 
gation of rootstocks from seed it would 
be necessary to purify such a hybrid in 
succeeding generations. Such a pro¬ 
cedure is costly both in time and re¬ 
sources. Add to this the possibility 
of sterility in the species cross, and the 
desirability of asexual propagation 
becomes more and more obvious. 
Even when breeding is not for disease 
resistance, uniformity is desirable. In 
propagating rootstocks from seed, uni¬ 
formity demands a homozygous parent 
tree. Relative homozygosity may be 
obtained in fruit trees with consider¬ 
able expenditures, but at the present 
time our knowledge as to the purity of 
different forms is rather meager. 
Hybrid vigor is utilized to consider¬ 
able advantage by corn growers and it 
should be of as great advantage to 
pomologists. To utilize hybrid vigor 
of the first generation in fruit trees it is 
necessary to be able to propagate the 
hybrid by asexual means. 
In order to test the relative merits of 
new types of scion wood derived from 
seedlings, they should be given uniform 
environmental conditions. Such uni¬ 
formity as to rootstocks could be best 
secured by asexual propagation of the 
rootstock. Perhaps such ' a critical 
study of scion wood derived from seed¬ 
lings which generally show great varia¬ 
bility would not interest the practical 
breeder, but what about bud varia¬ 
tions? Geneticists recognize two kinds 
of bud variations—first, modifications, 
and second, mutations. Modifications 
are ever present in fruit trees and are 
usually due to differences in combina¬ 
tions of environmental conditions, 
either internal or external, which 
existed during the development of that 
particular organ. Bud mutations, 
while comparatively rare, do occur in a 
large number of plants. Bud muta¬ 
tions are transmissible, while modifica¬ 
tions are not. In order to determine 
whether we are dealing with a bud 
mutation or a modification, except in 
very striking cases, such as the produc¬ 
tion of red plums on the branch of a 
yellow plum tree, we must test out the 
variation to see whether or not it will 
come true to type. Such a test de¬ 
mands uniform rootstocks best secured 
by asexual propagation. 
Cuttings of a large number of species 
and varieties were planted in February, 
1923, to ascertain how many would 
root readily from cuttings. It was 
necessary to terminate the experiment 
in May, 1923. The cuttings were 1 
foot long and from three-fifths to one- 
half inch in diameter. They were 
planted 10 inches deep, leaving about 
2 inches exposed. The soil was a 
light loam mixed with a greenhouse 
soil consisting of peat, leaf mold, sand, 
manure, and loam. The soil was kept 
moist throughout the course of the 
experiment which was conducted on a 
well-drained piece of land in Berkeley, 
Calif. The cuttings were obtained 
from the University Farm, Davis, 
Calif., the United States Plant Intro¬ 
duction Gardens, Chico, Calif., the 
Citrus Experiment Station, Riverside, 
Calif., and the Connecticut Agricul¬ 
tural Experiment Station, Storrs, Conn. 
The accompanying table lists the 
number of cuttings of each sample 
which formed leaves, shoots, callus, 
roots, of made no growth. Some of 
the cuttings formed either a callus or 
roots in all of the forms -listed in the 
table. A summary is given at the 
end of the table showing the species 
and varieties which failed to form 
either a callus or roots under the 
particular conditions of the experiment. 
From the review given in the first 
part of the paper and from the de¬ 
scription of the conditions of the ex¬ 
periment, the reader may conclude 
that experimental conditions were not 
EXPLANATORY LEGEND FOR PLATE 1 
Group 1: 
A. —Rooted cuttings of Prunus besseyi from Connecticut. 
B. — Prunus munsoniana from Connecticut. 
C. —Prunus pumila from Connecticut. 
Group 2: 
A.—Rooted cuttings of Cydonia oblonga, SPI 33214. 
B —Prunus bokhariensis, SPI 40229. 
Group 3: 
A. —Rooted cuttings of Satsuma plum, Davis 13-12. 
B. —Clyman plum, Davis 5-9. 
C. —Hamari fig, SPI 6468. 
D. —Fj Strawberry X Peento, peach hybrid Davis, 1-12 
