SOME STEM TUMORS OR KNOTS ON APPLE AND QUINCE TEEES. 



a twig, and may be noted at the end of the growing season. In 

 the form usually occurring on many other trees, the swellings appear 

 on twigs and limbs indiscriminately, apparently having no connec- 

 tion with the formation of buds. The tumors vary greatly in size 

 on the same and on different trees; some are as small as a pea; 

 others attain a size of 2 to 3 inches in diameter. This variation 

 in size is noted even at the beginning of the formation. Imma- 

 ture tumors are often formed on all por- 

 tions of the tree, quite frequently occurring 

 at the base of twigs (fig. 3) or springing 

 from older limbs or from the trunk. Dur- 

 ing the first period of their growth the 

 swellings are covered with a thick, fleshy 

 layer of meristem and bark tissues. The 

 growth for the first year or two is often 

 very rapid. At the end of a varying period 

 of time, usually one to three years, depend- 

 ing on the variety of the tree and the condi- 

 tions of growth in the locality Avhere it is 

 found, the bark covering the tumors be- 

 comes ruptured by the rapid formation in 

 the interior of a very peculiar structure; 

 the bark tissue ceases to grow, but the inte- 

 rior tissues develop a structure similar to 

 that found in root formation in the hairy- 

 root disease. As the bark breaks away, 

 small elevations, which resemble short 

 thickened root caps, appear on the surface 

 of the tumors, giving them a very warty ap- 

 pearance (fig. 4). The knots now resemble 

 the origin of the formation of the Avoolly- 

 knot form of hairj^-root described by the 

 writer" in a lecture to the National Nursery- 

 men's Association last year. 



The tumors in their older form in some 

 cases become hollowed out by a slight decay 

 of the tissue in the center, which results 

 either directly from the disease or from the entrance of Avood-rotting 

 organisms which are foreign to it. The mature form of these knots 

 (fig. 1) resembles greatly the outgrowths upon the limbs of a num- 

 ber of kinds of trees described by Sorauer ^ in Germany under the 



Fig. o. — Yuuug tumors form- 

 ing at the base of twigs on 

 a Charlamoff apple tree at 

 Fayetteville, Ark. 



aHedgcock, George G. Prevention of Apple Crown-Gall and Hairy-Root. 

 National Nurseryman, vol. 15, pp. ] 92-193, 1907. American Fruits, yol. 7, p. 

 69, 1907. Apple Specialist, vol. 4, pp. 14-15, 1907. 



^ Sorauer, P. Kropfmaser. Handbucli der Pflanzenkrankheiten, vol. 1, pp. 

 731-734 and fig. 38, 1S86. 

 [Cir. 3] 



