Читать книгу Manual of American Grape-Growing - U. P. Hedrick - Страница 68

If bench grafts are planted at once in the nursery, most of them fail. They are, therefore, stratified in a callusing bed where moisture and temperature can be controlled. Bioletti describes a callusing bed and its use as follows:[6]

"This callusing bed is usually a pile of clean sand placed on the south side of a wall or building and surrounded by a board partition where there is no possibility of its becoming too wet by the flow of water from a higher level or from an overhanging roof. It should be protected, if necessary, by a surrounding ditch. It should be furnished with a removable cover of canvas or boards to protect it from rain and to enable the temperature to be controlled by the admission or exclusion of the sun's rays. A water-proof wagon-cover, black on one side and white on the other, is excellent for this purpose.

"The bottom of the callusing bed is first covered with 2 or 3 inches of sand. The bundles of grafts are then placed in a row along one end of the bed, and sand well filled in around them. The bundles should be placed in a slightly inclined position with the scions uppermost, and the sand should be dry enough so that it sifts in between the grafts in the bundle. The bundles of grafts are then covered up completely with sand, leaving it at least 2 inches deep above the top of the scion. Another row is then placed in the same manner until the bed is full. Finally a layer of 2 or 3 inches of moss or straw is placed over all.

"In the callusing bed we should endeavor to hasten and perfect the union of stock and scion as much as possible while delaying the starting of the buds and the emission of the roots. The latter processes require more moisture than the formation of healing tissue, therefore the sand should be kept comparatively dry. Between 5 and 10 per cent of water in the sand is sufficient. The purer the sand the less water is necessary. There should be a little more moisture present than in the sand used for keeping the cuttings over winter. Too much moisture will stimulate the emission of roots and starting of buds without aiding the callus formation.

"All the vital processes progress more rapidly when the cuttings are kept warm. To delay them, therefore, we keep the sand cool, and to hasten them we make it warm. In the beginning of the season and up to the middle of March we keep the sand cool. This is done by keeping the bed covered during the day when the sun is shining, and uncovering occasionally at night when there is no fear of rain. If the black-and-white wagon-cover is used, the white side should be placed outward to reflect the heat. The temperature should be kept about 60° F. or lower.

"About the middle of March the temperature of the bed should be raised. This is done by removing the cover during warm days and carefully covering at night. If necessary the layer of moss or straw should be removed on sunny days and then replaced. The temperature of the sand at the level of the unions should be about 75° F. during this period. If the temperature rises higher than this, there will be a more abundant production of callus, but it will be soft, easily injured, and liable to decay.

"At the end of four weeks after warming the bed, the union should be well cemented. The callus should not only have formed copiously around the whole circumference of the wound, but it should have acquired a certain amount of toughness due to the formation of fibrous tissue. It should require a pull of several pounds to break the callus and separate stock and scion. When the callus has acquired this quality the grafts are in condition to be planted in the nursery, and may be handled without danger. If taken from the bed while the callus is still soft, many unions will be injured and the grafts will fail, or unite only on one side.

"If left as long as this in the callusing bed most of the scion buds will have started and formed white shoots. These shoots, however, should not be more than 1/2 to 1 inch long. If they are longer the bed has been kept too wet or too warm. Roots will also have started from the stock, but these also should not be over 1/2 inch long. The grafts should be handled as carefully as is practicable, but there is no objection to breaking off any scion shoots or stock roots which have grown too long. It is almost impossible to save them, and new ones will start after the grafts are planted, and make a perfectly satisfactory growth."