and, 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 the great majority of the trees in the grove come out in full leaf.
But there are frequently trees still leafless after the nuts on the
early individuals are of the size of a marble. This variation in the
blooming season has considerable economic 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.

_Foliage Characteristics_

The character of the foliage varies from the broad-leaved types, whose
foliage somewhat resembles that of the horse-chestnut, to the
narrow-leaved varieties whose leaves have a tendency to curl up like the
foliage of the Winesap apple. The broad-leaved types are much more
densely foliated 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 injury. 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 types often appear to have less blight on the nuts and leaves
because of their exposure to the sunshine.

_Disease Resistance_

Probably one of the most important limiting factors in walnut production
in California, and especially in the older walnut sections, is the
bacterial disease commonly known as walnut blight. The inroads of this
disease have caused a very heavy dropping of the nuts during many
seasons of the past, and although a great deal of time and scientific
effort has been devoted to the control of the trouble, there is no
satisfactory known means for the prevention of walnut blight at the
present time.

It is a well-known fact that in the vegetable kingdom closely related
species suffer in different degrees from the attacks of the same
parasite. This difference in resistance is often as marked among
different varieties of the same species as between the species
themselves. The absence of blight is not necessarily an indication of
immunity. There is a great deal of difference in the amount of b