rees need. Nitrogen,
phosphorus, and potash, also magnesium are needed. We are taking more
from the soil than we are putting back."

Corsan: "In Cuba there are hundreds of sharks. These make fine manure,
wonderful for nut trees."

Prof. Slate: "How many sharks would you need for an acre of land?"

Morphology and Structure of the Walnut

C. C. LOUNSBERRY, Iowa State College

This subject, the structure of the walnut, is discussed in its relation
to propagation. Catkin bearing nut trees, such as the walnut, have a
refined structure that makes grafting difficult. Structure, rather than
form of walnuts, suggests treatment under the headings, bark, cambium,
wood, roots, pith and buds, as well as the sap that permeates them.

=Bark:= When the bark of the walnut is cut, as in budding, it is difficult
to tie down so it will not curl and yet not strangle the bud. The
wax-like covering of the bark is thin. However, the bark itself will
stay green two months or more if weather is cool.

=Cambium:= The cambium dries quickly when exposed to air, and must be kept
covered. Grafted walnuts show callus growth from the cambium, and also
from the pith of stems and the endodermis of the root.

=Wood:= The wood of the walnut is diffuse porous, brittle, straight
grained, and easily split. The wood must be cut diagonally to get
sufficient tension to hold the scion in grafting. The branch grows
rapidly in a short season, May 15th to July 1st in central Iowa. The
upper two-thirds of the one year growth is usually light weight with
pith of large diameter. The base of the one-year growth is the best for
scions. Some varieties of walnut as for example the Thomas, have
relatively large one-year growth and more scions can be cut from its
branches than from the wood of Ohio which is small and willow-like.

Measurements taken in 1940 on 118 common black walnut seedlings planted
in 1939 showed 9/16" average diameter of seedling at crown, 5/16"
average diameter of pith at crown; 3/8" average diameter of seedling at
top; and 1/4" average diameter of pith at top; 3.26 inches average
length of solid pith above crown; 2.91 inches average length of solid
pith in root below crown.

=Pith:= Pith in the black walnut is chambered (lamellate) in the older
wood, but solid in the younger, growing wood. The plates are a light
brown color, getting larger in diameter toward the top of the year's
growth. The leaf traces from the leaf rachis to the pi