EFFECT OF THE DISEASE ON APPLE TREES. 30 
result of the opinion expressed by Toumey (68) concerning crown- 
gall of the almond, who proved that it may be highly contagious and 
extremely destructive. 
Beginning with the date of Toumey’s paper on crown-gall of the 
almond, without waiting for further proof, the general assumption 
has been that the effect of crown-gall upon the apple tree is identical 
with that of this disease upon the almond. With the general opinion 
prevalent in most parts of the country, vigorous methods have been 
advocated very generally by pathologists, entomologists, nursery 
inspectors, and others. Stringent laws have been enacted for stamp- 
ing out the disease, with the assumption that the disease of the apple 
is as injurious as that of the stone fruits. 
In summing up the few opinions which were given from actual 
experiments, it may be well to suggest that in all probability the 
effect of root-rot has been confused with that of crown-gall. It is 
well known that root-rot attacks orchards in many portions of the 
apple-growing belt, especially in the South and the Southwest. In 
collecting accurate data on the effect of crown-gall and hairy-root it 
is absolutely necessary that each individual tree be examined and 
the condition of the roots noted before drawing any conclusions as 
to the cause of the death. A study of the connection between root- 
rot and crown-gall is also necessary. Al! of the trees in the orchard 
experiments of the writer have been free from root-rot, but borers 
were present in orchards 1 and 2 and killed all of the trees that died 
after the first year, but attacked healthy and diseased trees alike. In 
forming conclusions as to the cause of the death of an apple tree, not 
only root-rot but also these borers should be taken into account, 
since they apparently attack smooth-rooted trees as often as those 
diseased with crown-gall and hairy-root. These insects bore beneath 
the bark into the wood of the tree and allow root-rot fungi to enter 
the wounds made by them. Quite often death results in a couple of 
years from the first attack. 
Wherever an orchard has been reported as dying in a short time 
from crown-gall it will be well to look deeply into the causes of the 
death of the trees before accepting the report as a scientific fact. In 
the writer’s opinion, which is based upon exact orchard experiments, 
crown-gall never kills an apple tree suddenly, and where no other dis- 
turbing factor enters, it may not be able to kill it at all. The wound- 
ing of a projecting hard or soft gall may enable wood-rotting organ- 
isms to enter the tree and kill it. Again, the presence of gall tissues 
may the better enable insects to attack the tree, but in the writer’s 
experiments he found no proof that diseased trees were more subject 
than healthy trees to the attacks of insects and wood-rotting fungi. 
50414°—Bul. 186—10——3 
