THE HANDLING OF THE PLANTS - Continued
Repairing street trees.
[Illustration: Fig. 161. A wound, made by freezing, trimmed out and
filled with cement.]
The following advice on "tree surgery" is by A.D. Taylor (Bulletin 256,
Cornell University, from which the accompanying illustrations are
adapted):--
"Tree surgery includes the intelligent protection of all mechanical
injuries and cavities. Pruning requires a previous intimate knowledge of
the habits of growth of trees; surgery, on the other hand, requires in
addition a knowledge of the best methods for making cavities air-tight
and preventing decay. The filling of cavities in trees has not been
practiced sufficiently long to warrant making a definite statement as to
the permanent success or failure of the operation; the work is still in
an experimental stage. The caring for cavities in trees must be urged as
the only means of preserving affected specimens, and the preservation of
many noble specimens has been at least temporarily assured through the
efforts of those practicing this kind of work.
[Illustration: Fig. 160. A cement-filled cavity at the base of a tree.]
"Successful operation depends on two important factors: first, that all
decayed parts of the cavity be wholly removed and the exposed surface
thoroughly washed with an antiseptic; second, that the cavity, when
filled, must be air tight and hermetically sealed if possible. Trees are
treated as follows: The cavity is thoroughly cleaned by removing all
decayed wood and washing the interior surface with a solution of copper
sulfate and lime, in order to destroy any fungi that may remain. The
edges of the cavity are cut smooth in order to allow free growth of the
cambium after the cavity is filled. Any antiseptic, such as corrosive
sublimate, creosote, or even paint, may answer the purpose; creosote,
however, possesses the most penetrating powers of any. The method of
filling the cavities depends to a great extent on their size and form.
Very large cavities with great openings are generally bricked on the
outside, over the opening, and filled on the inside with concrete, the
brick serving the purpose of a retaining wall to hold the concrete in
place. Concrete used for the main filling is usually made in the
proportion of one part good Portland cement, two parts sand, and four
parts crushed stone, the consistency of the mixture being such that it
may be poured into the cavity and require little or no tamping to make
the mass solid. (Fig. 160.)
"Fillings thus made are considered by expert tree surgeons to be a
permanent preventive of decay. The outside of the filling is always
coated with a thin covering of concrete, consisting of one part cement
to two parts fine sand. Cavities resulting from freezing, and which,
though large on the inside, show only a long narrow crack on the
outside, are most easily filled by placing a form against the entire
length of the opening, having a space at the top through which the
cement may be poured (Fig. 161). Another method of retaining the
concrete is to reinforce it from the outside by driving rows of spikes
along the inner surface of either side of the cavity and lacing a stout
wire across the face of the cavity. For best results, all fillings must
come flush with the inner bark when finished. During the first year,
this growing tissue will spread over the outer edge of the filling, thus
forming an hermetically sealed cavity. In the course of time, the
outside of small or narrow openings should be completely covered with
tissue, which buries the filling from view.
[Illustration: Fig. 162. Bridge-grafting or in-arching from saplings
planted about the tree.]
"It has been found that there is a tendency for portland cement to
contract from the wood after it dries, leaving a space between the wood
and the cement through which water and germs of decay may enter. A
remedy for this defect has been suggested in the use of a thick coat of
tar, or an elastic cement which might be spread over the surface of the
cavity before filling. The cracking of portland cement on the surface of
long cavities is caused by the swaying of trees during heavy storms, and
should not occur if the filling is correctly done.
[Illustration: Fig. 163. Faulty methods of bracing a crotched tree. The
lower method is wholly wrong. The upper method is good if the bolt-heads
are properly counter-sunk and the bolts tightly fitted; but if the
distance between the branches is great, it is better to have two bolts
and join them by hooks, to allow of wind movements.]
"In addition to the preservation of decayed specimens by filling the
cavities, as above outlined, it has been proposed to strengthen the tree
by treating it as shown in Fig. 162. Young saplings of the same species,
after having become established as shown, are grafted by approach to the
mature specimen.
"Injury frequently results from error in the method of attempting to
save broken, or to strengthen and support weak branches that are
otherwise healthy. The means used for supporting cracked, wind-racked,
and overladen branches which show a tendency to split at the forks are
bolting and chaining. The practice of placing iron bands around large
branches in order to protect them has resulted in much harm; as the tree
grows and expands, such bands tighten, causing the bark to be broken and
resulting after a few years in a partial girdling (Fig. 163).
[Illustration: Fig. 164. Trees ruined to allow of the passage of
wires.]
[Illustration: Fig. 165. Accommodating a wall to a valuable tree.]
[Illustration: Fig. 166. The death of a long stub.]
[Illustration: Fig. 167. Bungling pruning.]
[Illustration: Fig. 168. The proper way to saw off a large limb. A cut
is first made on the under side to prevent splitting down; then it is
cut on the upper side. Then the entire "stub" is removed close to
the trunk.]
"To bolt a tree correctly is comparatively inexpensive. The safest
method consists in passing a strong bolt through a hole bored in the
branch for this purpose, and fastening it on the outside by means of a
washer and a nut. Generally the washer has been placed against the bark
and the nut then holds it in place. A better method of bolting, and one
which insures a neat appearance of the branch in addition to serving as
the most certain safeguard against the entrance of disease, is to
counter-sink the nut in the bark and imbed it in portland cement. The
hole for the sinking of the nut and washer is thickly coated with lead
paint and then with a layer of cement, on which are placed the nut and
washer, both of which are then imbedded in cement. If the outer surface
of the nut be flush with the plane of the bark, within a few years it
will be covered by the growing tissue.
[Illustration: Fig. 169. A weak-bodied young tree well supported;
padding is placed under the bandages.]
[Illustration: Fig. 170. The wrong way of attaching a guy rope.]
[Illustration: Fig. 171. An allowable way of attaching a guy rope.]
[Illustration: Fig. 172. The best way of attaching a guy rope, if a tree
must be used as support.]
"The inner ends of the rods in the two branches may be connected by a
rod or chain. The preference for the chain over the rod attachment is
based on the compressive and tensile stresses which come on the
connection during wind storms. Rod connections are preferred, however,
when rigidity is required, as in unions made close to the crotch; but
for tying two branches together before they have shown signs of
weakening at the fork, the chain may best be used, as the point of
attachment may be placed some distance from the crotch, where the
flexibility factor will be important and the strain comparatively small.
Elms in an advanced stage of maturity, if subjected to severe climatic
conditions, often show this tendency to split. These trees,
especially, should be carefully inspected and means taken to preserve
them, by bolting if necessary."
[Illustration: Fig. 173. A method of saving valuable trees along streets
on which heavy lowering of grade has been made.]
The illustrations, Figs. 164-173, are self-explanatory, and show poor
practice and good practice in the care of trees.
[Illustration: IX. A rocky bank covered with permanent informal
planting.]
The grafting of plants.
Grafting is the operation of inserting a piece of a plant into another
plant with the intention that it shall grow. It differs from the making
of cuttings in the fact that the severed part grows in another plant
rather than in the soil.
There are two general kinds of grafting--one of which inserts a piece of
branch in the stock (grafting proper), and one which inserts only a bud
with little or no wood attached (budding). In both cases the success of
the operation depends on the growing together of the cambium of the cion
(or cutting) and that of the stock. The cambium is the new and growing
tissue lying underneath the bark and on the outside of the growing wood.
Therefore, the line of demarcation between the bark and the wood should
coincide when the cion and stock are joined.
The plant on which the severed piece is set is called the stock. The
part which is removed and set into the stock is called a cion if it is a
piece of a branch, or a "bud" if it is only a single bud with a bit of
tissue attached.
The greater part of grafting and budding is performed when the cion or
bud is nearly or quite dormant. That is, grafting is usually done late
in winter and early in spring, and budding may be performed then, or
late in summer, when the buds have nearly or quite matured.
[Illustration: Fig. 174. Budding. The "bud"; the opening to receive it;
the bud tied.]
The chief object of grafting is to perpetuate a kind of plant which will
not reproduce itself from seed, or of which seed is very difficult to
obtain. Cions or buds are therefore taken from this plant and set into
whatever kind of plant is obtainable on which they will grow. Thus, if
one wants to propagate the Baldwin apple, he does not for that purpose
sow seeds thereof, but takes cions or buds from a Baldwin tree and
grafts them into some other apple tree. The stocks are usually obtained
from seeds. In the case of the apple, young plants are raised from seeds
which are secured mostly from cider factories, without reference to the
variety from which they came. When the seedlings have grown to a certain
age, they are budded or grafted, the grafted part making the entire top
of the tree; and the top bears fruit like that of the tree from which
the cions were taken.
There are many ways in which the union between cion and stock is made.
Budding may be first discussed. It consists in inserting a bud
underneath the bark of the stock, and the commonest practice is that
which is shown in the illustrations. Budding is mostly performed in
July, August, and early September, when the bark is still loose or in
condition to peel. Twigs are cut from the tree which it is desired to
propagate, and the buds are cut off with a sharp knife, a shield-shaped
bit of bark (with possibly a little wood) being left with them (Fig.
174). The bud is then shoved into a slit made in the stock, and it is
held in place by tying with a soft strand. In two or three weeks the bud
will have "stuck" (that is, it will have grown fast to the stock), and
the strand is cut to prevent its strangling the stock. Ordinarily the
bud does not grow until the following spring, at which time the entire
stock or branch in which the bud is inserted is cut off an inch above
the bud; and the bud thereby receives all the energy of the stock.
Budding is the commonest grafting operation in nurseries. Seeds of
peaches may be sown in spring, and the plants which result will be ready
for budding that same August. The following spring, or a year from the
planting of the seed, the stock is cut off just above the bud (which is
inserted near the ground), and in the fall of that year the tree is
ready for sale; that is, the top is one season old and the root is two
seasons old, but in the trade it is known as a one-year-old tree. In the
South, the peach stock may be budded in June or early July of the year
in which the seed is planted, and the bud grows into a saleable tree the
same year: this is known as June budding. In apples and pears the stock
is usually two years old before it is budded, and the tree is not sold
until the top has grown two or three years. Budding may be performed
also in the spring, in which case the bud will grow the same season.
Budding is always done on young growths, preferably on those not more
than one year old.
[Illustration: Fig. 175. Whip-graft.]
Grafting is the insertion of a small branch (or cion), usually bearing
more than one bud. If grafting is employed on small stocks, it is
customary to employ the whip-graft (Fig. 175). Both stock and cion are
cut across diagonally, and a split made in each, so that one fits into
the other. The graft is tied securely with a string, and then, if it is
above ground, it is also waxed carefully.
[Illustration: Fig. 176. Cleft-graft before waxing.]
In larger limbs or stocks, the common method is to employ the
cleft-graft (Fig. 176). This consists in cutting off the stock,
splitting it, and inserting a wedge-shaped cion in one or both sides of
the split, taking care that the cambium layer of the cion matches that
of the stock. The exposed surfaces are then securely covered with wax.