THE IMPROVEMENT OF 
ROOT-STOCKS USED IN FRUIT 
PROPAGATION 
H. J. WEBBER 
Director, California Agricultural Experiment Station, Berkeley 
OR many years it has been clearly 
recognized that the root-stock 
has an important influence on 
the scion and on the quantity and 
quality of the crop produced, yet 
very little experimentation has been 
devoted to root-stock problems or to 
the determination of the best stocks to 
use. 
It is true that these matters are dis- 
cussed at almost every convention of 
fruit growers and much information 
based on experience has been recorded. 
In general, the discussion and indeed 
all consideration has been limited to 
the effect on different varieties of cer- 
tain root-stocks which are themselves 
usually very variable species. In cit- 
rus fruits, for instance, all considera- 
tion has been limited to a discussion of 
whether one should use sour orange 
(Citrus aurantium), sweet orange (Cit- 
rus sinensis), grapefruit (Citrus gran- 
dis), lemon (Citrus limonia) or trifoliate 
orange (Poncirus trifoliata). These spe- 
cies are not composed of stable, uni- 
form groups of individuals but are ex- 
ceedingly variable, each containing 
many hundreds of different types. No 
attention has been given, however, to 
the reactions that may be expected 
from the use of different types within 
the species. The same statement ap- 
plies equally well to the various stocks 
used for apples, peaches, pears and 
similar fruits. 
It seems clear to the writer that this 
is fundamentally wrong, and yet be- 
fore any generally accepted policy can 
be overthrown, evidence must be found 
definitely to show that itis wrong. The 
writer for the last five years has been 
engaged in the study of this problem in 
connection with citrus fruits and the 
evidence obtained will probably apply 
just as definitely to other fruits as to 
citrus. The following is an outline of 
the experiments and results of a study 
of this problem with different varieties 
of citrus.! 
VARIATIONS IN NURSERY AND ORCHARD 
TREES 
Citrus orchards show great variation 
in the yield of different trees in the 
same orchard. This variation is known 
to be universal even in orchards of the 
same variety that have been planted 
with the best obtainable trees. Some 
orchards are quite uniform, however, 
while others are exceedingly variable. 
Batchelor and Reed have shown? that 
the trees in the most uniform groves 
will vary from 30 to 40 percent of the 
mean. 
Mr. A. D. Shamel and his associates 
of the U. S. Department of Agriculture 
have emphasized the relation of the 
character of the buds used in propaga- 
tion to this variability in the orchard 
and have rightly urged the importance 
of choosing buds for propagation from 
uniformly high yielding trees known to 
produce only fruits of standard type.’ 
Is this the only factor involved? 
It is a well known fact that nursery 
trees as they are normally grown when 
two years old and ready for sale ex- 
hibit great diversity in size, the trunks 
frequently ranging from 34 inch to 14% 
inches in diameter. Does this varia- 
tion in size of trees of the same age 
‘Webber, H. J.Selection of stocks in citrus propagation, California Agricultural Experiment 
Station Bulletin 317, January, 1920. 
*Batchelor, L. D. and Reed, H. S. Unpublished investigations. 
%3Shamel, A. D. et al. 
Citrus fruit improvement, U.S. Department of Agriculture Bulletin 623, 
July 22, 1918; Bulletin 624, July 25, 1918; Bulletin 697, Sept. 27, 1918 and Farmers’ Bulletin 794. 
291 
