PREVENTION AND CURE. . 67 
For the proper development of callus in apple grafts, as already 
mentioned, it was found that sand was the best material for packing. 
The materials used in the experiment were steam sterilized. It will 
not be easy to thoroughly sterilize sand in the nursery unless improved 
machinery is invented, but with a little ingenuity in the arrangement 
of perforated steam pipes through the sand container, whether it be 
a box or a bin, most of the sand in use can be sterilized. Moss or 
excelsior can wate be sterilized more or less thoroughly by putting 
it in a barrel or box and passing through it live steam from a pipe. 
This will rid the packing material of fungi, a number of which are 
found attacking grafts improperly stored. Two such fungi are cer- 
tainly species of Botrytis and Fusarium. 
TIME OF PLANTING ROOT GRAFTS. 
Tf root grafts are put in cold storage they can be held in good 
condition till the proper time for planting in the spring. If the 
facilities for holding back growth in root grafts are poor, then early 
planting is necessary. Do not allow the root grafts to form exces- 
sive callus and start to grow (Pl. VIII, fig. 2). In the writer’s 
experiments the highest percentage of crown-gall occurred under 
such conditions. 
CARE IN THE CULTIVATION OF TREES IN THE NURSERY. 
It has been shown that root grafts acquire crown-gall chiefly 
during the first season’s growth and that much of the crown-gall 
(Pl. II, fig. 3) and woolly-knot (Pl. VI, fig. 5) on certain varieties, 
such as the Wealthy, occurs on the scion portion of grafted trees 
near the surface of the soil. An examination of such galls usually 
shows the presence of a wound in the tissues at the base of each. 
This wound was evidently made with a hoe in cutting out weeds in 
the row while the trees were young. For this reason care should be 
taken to avoid wounding trees in cultivation. 
When apple seedlings have been budded care should be taken not 
to ridge the dirt about the trees until the bud wounds have at least 
partially healed. If the trees are cultivated immediately after bud- 
ding, crown-gall is often communicated to the callus forming in the 
fresh wound. It is better to cultivate a short time before budding 
rather than just after. 
SELECTION OF HEALTHY TREES FOR THE SCION ORCHARD NECESSARY. 
The matter of securing healthy scions for root grafting is impor- 
tant, as has been shown by the experiments with apparently healthy 
scions taken from trees with the roots diseased with crown-gall and 
hairy-root. It was shown that the use of such scions increased the 
amount of disease present in root-grafted trees (see pp. 23 and 25). 
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