30 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE. ~ 
and even the smaller units or variations combined in these sets, with 
very few exceptions, gave the same results. None of these excep- 
tions varied widely from the general trend of the results. <A refer- 
ence to the tabular results of a number of other experiments given 
both earlier and later in this bulletin will lead to the same conclusions 
as are drawn from Table XIV. 
EFFECT OF THE DISEASE UPON APPLE TREES. 
OBSERVATIONS BY OTHERS ON CROWN-GALL. 
It has generally been held by pathologists that crown-gall is very 
destructive to trees. Frank (14), in discussing the Wurzelkropf on 
apple trees in Germany, notes that trees with very large galls show 
a weaker growth of the trunk and branches, probably due to the fact 
that the swellings absorb considerable nutritive substance. Wickson 
(77), in discussing the general subject of root knots on fruit trees, 
makes the following statement: 
Probably during the last twenty years hundreds of thousands of such trees (referring 
to trees with galls) have split and died in the best soil and with the best treatment. 
If disease has stunted the growth of a young tree, pluck it out and plant a new one. 
If the knots are found on larger trees which are making satisfactory growth in spite 
of them, remedial measures should be tried. The final result seems to depend upon 
whether the natural or the diseased growth secures ascendancy early in the life of the 
tree; but apricot trees have been taken up after thirty years of satisfactory growth 
and bearing and found to have roots badly affected with the knots. 
In the same bulletin Woodworth makes this statement: 
The presence of a gall at the crown of the plant seems to effect an obstruction to 
the flow of the sap, and in this way a tree or vine becomes weakened and finally dies. 
The gall generally attacks small plants, but not always, and it often takes a number of 
years before the plant is killed. 
Yates (80), in speaking of the crown-gall, does not consider the 
same a disease. 
Selby (50), referring to apple crown-gall, says: ‘‘It seems unlikely 
that such affected trees will be worth planting, and all of them suffer- 
ing with this trouble should be burned.” 
Stewart, Rolfs, and Hall (64), make the following statement: **We 
find crown-gall not uncommon on apple trees in the nurseries in 
western New York, but we know of no case where it has caused 
material loss. * * * Wewould recommend that all trees showing 
the least trace of the disease be rejected; for, although we have never 
seen any ill effects from the planting of affected apple trees, it appears 
probable that the disease may thus be spread.’’ They refer to a 
nurseryman who writes that he planted a row of healthy apple trees 
and at the same time a row of trees affected with crown-gall, and 
who states that after two years the trees with the crown-gall had made 
just as good a growth as the healthy trees near by. 
186 
