62 The Journal 
of these groves are the progeny of 
especially selected trees known to have 
considerable merit. On the other hand, 
it is very apparent that many of them 
are the result of a great demand for 
seedling trees when this industry was in 
its infancy twenty or thirty years ago. 
At that time great quantities of walnuts 
were planted without due regard for 
their parentage. Again, there is a wide 
range of variability among the individual 
trees of any grove, as variations in 
type of tree, blooming season, character 
of foliage, resistance to disease, pro- 
ductivity and character of the nuts. 
Type of Tree.—The tree types vary 
from the upright sturdy individual to 
the more or less spreading, weeping 
types, which droop nearly to the ground 
under the burden of their crop. The 
upright, vigorous growing type is well 
exemplified in the Eureka. On the 
other hand such varieties as the Prolific 
have a spreading, bushy habit, and an 
almost semi-dwarfness characterizes 
their growth. 
Blooming Season.—It is not unusual to 
find the blooming season in an ordinary 
seedling grove extending over a period 
of from a month to six weeks. <A few 
individual trees leaf out and blossom 
with the first signs of spring. Then 
quite the larger part of the grove comes 
out in full leaf, while there are frequently 
trees which are still bare after the nuts 
on the early individuals are of the size 
of a marble. This variation in the 
blooming season has considerable econ- 
omic importance in relation to the 
harvesting and marketing of the nuts 
as well as the avoidance of diseases 
and frost which may be more prevalent 
during certain periods in the spring. 
MANY TREES UNPROFITABLE 
Variation in Productivity.—Some of 
the old experienced walnut growers feel 
that 25% of their seedling trees are un- 
profitable, another 25% are barely pay- 
ing expenses, and that the profit is 
really derived from about 50% of the 
trees. The variations in seedling trees 
is well shown by Smith? in summarizing 
the results of certain fertilizer tests; he 
2 Calif. Bull. 231, p. 187, 1912. 
of Heredity 
found that twenty trees in a given row 
varied in productivity as follows: Num- 
ber of pounds produced by each tree, 
1, 16, 45, 10, 21, 97, 20,8, 26, 0, 16, 1a 
13, 10, 21, 2, 31, 7, 14. This is only 
fair example of the variation in the large 
majority of seedling groves. The above 
figures are from a young grove and 
should not be considered as typical of 
the total production for twenty mature 
walnut trees. 
Foliage Characters.—The character of — 
the foliage varies from the broad-leaved 
types, in which case the foliage somewhat 
resembles that of the horse-chestnut, to 
the narrow-leaved varieties whose leaves 
have a tendency to curl up like the foli- 
age of the Winesap apple. The broad- 
leaved types are much more densely foli- ~ 
ated and this factor has considerable 
bearing on the problems of sun-scald on 
the twigs and trunks of the tree and the 
exposure of the nuts to this malady. 
For this reason, the densely foliated 
varieties may prove best adapted to the 
inland valleys, where the difficulties of 
sun-scald are most prevalent. The 
more sparsely foliated sorts often appear 
to have less blight on the nuts and leaves, 
because of their exposure to the sun- 
shine. 
Disease Resistance.—Probably one of 
the most important limiting factors to 
walnut production in California, and es- 
pecially in the older walnut sections, is 
the bacterial disease commonly known 
as walnut blight. The inroads of this 
disease have caused a very heavy drop- 
ping of the nuts during many seasons of 
the past, and although a great deal of 
time and scientific effort have been de- 
voted to the control of this trouble, 
there is no known means for the preven- 
tion of walnut blight at the present 
time. 
The great variation among seedling 
trees in regard to their susceptibility to 
blight is indeed a hopeful sign for the 
eventual production of varieties which 
will more or less resist this malady. 
Among 105 trees in an orchard under ob- 
servation in Orange County, the per- 
centage of diseased nuts on the indi- 
vidual trees before any dropping had 
Se ee eee eee eee ee ae ee eee ee eee ae 
