WRAPPING APPLE GRAFTS AND ITS RELATION TO CROWN-GALL. 17 



in the majorit}^ of cases. It had, however, exerted no injurious effect, 

 because, as the 3'oung trees had grown in diameter, the rubber had 

 expanded. The roots had frequent!}^ punctured the rubber freel3^ 

 In other words, the rubber had in no way retarded the growth. The 

 unions formed under the rubber were smooth and even; in fact, they 

 were the most perfect of all those formed in the experiment. The 

 rubber covering was practically waterproof. So perfect were the 

 unions that in many cases it was possible to detect the line of demar- 

 cation between the root and scion onl}^ by the difference in color. 



Waxed paper. — When planted in the spring the waxed paper had not 

 rotted, but it had a tendency to become unrolled, due probably to too 

 much oil in the Avax. When dug in the autumn the paper had mostly 

 disappeared. The grafts showed many smooth trees, but the percentage 

 was not nearly so large as in the case of those wrapped with rubber or 

 cloth. Attention should be called to the fact that in all grafts where 

 wax was used the wax itself seemed to exert an unfavorable effect on 

 the union, and the writers are inclined to discourage its use wherever 

 it comes into direct contact with wounded surfaces. 



Plain thread. — When planted in the spring the plain thread had in 

 many instances entirely rotted away. The grafts when dug showed 

 many callus proliferations. The percentage of smooth grafts was low 

 when compared with rubber or cloth wrappings. The results were 

 about as good as those secured by the use of waxed paper wrapping, 

 and a little better than those obtained with waxed thread. 



Waxed thread. — When the grafts were planted the waxed thread was 

 intact. When dug in the autumn the grafts showed from 6 to 8 per 

 cent with knots caused b}^ the pressure exerted by the thread, which 

 had not rotted away because the wax protected it more or less. The 

 percentage of smooth trees aside from this was almost the same as for 

 the plain thread. No perceptible advantage appeared to be gained by 

 the use of waxed thread as compared with plain thread. 



Plain thread with uniomo axed. — At the time of planting it was noted 

 that the wax had in many instances penetrated between the surface of 

 the two pieces. The callus had formed in irregular masses, there being- 

 nothing to confine it. It furthermore appeared as if the wax had exerted 

 the unfavorable effect already referred to in connection with the use of 

 waxed paper. When dug the trees in the majority of instances showed 

 thread knots, due no doubt to the fact that the wax had retarded the 

 rotting away of the thread. The unions were usually rough. The 

 unfavorable effect ascribed to the wax was evident not only in the 

 immediate wound areas, but also all along the bark on both scion and 

 root pieces, wherever the wax came in contact with the tissue. 



Uniorai^jyed grafts. — The grafts with no wrapping showed the excess- 

 ive development of callus more than any others. However, many of 

 18270— No. 100—07 2 



