40 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE. 
since planting only 8 trees have died, in spite of the fact that the trees 
have been twice transplanted. Out of 225 healthy trees, 3 have died; 
of 82 trees diseased with hairy-root, 2 have died; and of 193 trees 
diseased with crown-gall, 3 have died, the percentage being but 
slightly in favor of the healthy trees. This difference is so small as 
to depend entirely on chance. 
The experiments mentioned, as well as observations made in other 
orchards, indicate that the mere presence of the forms of crown-gall 
or of hairy-root at or near the crown of an apple tree, in the orchard 
has very little effect on the subsequent growth of the tree, provided it 
has a well-developed root system. 
Observations made on badly diseased trees growing elsewhere 
under poor soil conditions indicate that where either hard or soft galls 
extend entirely around the main root of a tree, unless it is able to 
throw out roots above such growths, a marked stunting effect may 
follow. A grafted tree of this character can not develop into a good 
tree unless it can form roots on the scion portion above the union. 
It is inadvisable on general principles to plant any trees affected by 
a contagious disease like crown-gall, and particularly so with varie- 
ties that do not root well from the scion. Trees of the following 
varieties are more likely to overcome a mild attack of crown-gall, as 
they are better able to root from the scion: Ben Davis, Wolf River, 
Northern Spy, Grimes, Gano, Northwestern Greening, Missouri, 
Wealthy, Walbridge, Fameuse, and Salome. 
The following statement made by Wickson (77) fully meets the 
views of the writer and applies to hairy-root as well as to crown-gall: 
If the diseased growth is so extensive during the early period of the life of the tree 
as to stunt the development of the root system, no favorable results can be expected 
during the later period of development of such a tree. It is fortunate that nursery 
trees are generally dug and sold at a period when the stunting effect of these diseases 
is most marked. 
The same statement might be made of many poorly rooted trees 
which have not formed a perfect union between scion and root piece 
in the root graft and as a result have a defective root system, irrespec- 
tive of these diseases. These constitute a considerable loss to the 
- nurseryman where poorly fitted root grafts are used. 
These statements apply to both hard and soft crown-gall and to all 
of the forms of hairy-root found in the nursery. The results of the 
investigation indicate very clearly that apple trees are able to resist 
the effects of these forms of disease in the orchard, and their impor- 
tance has been greatly overrated. 
It must not be understood, however, that trees diseased with even 
the milder forms of crown-gall and hairy-root are fully as valuable 
for planting as healthy trees. They can certainly not be rated as 
186 
