CAUSE AND NATURE OF CROWN-GALL 



33 



all the plants cited above are caused by the same organism or 

 by closely related parasites still remains unsettled. 



THE STRUCTURE AND DEVELOPMENT OF THE GALL. 



The crown-gall is usually annual in its period of growth. 

 The galls ordinarily begin their growth in the spring and ma- 

 ture in the fall. Those, however, which begin to develop late 

 in the summer or during the fall months nearly always in this 

 climate continue their growth throughout the winter, even when 

 the normal tissue of the tree is dormant. 



Specimens of nine months old 

 almond seedlings having young galls 

 upon them no larger than small peas 

 were heeled in in October, and when 

 these plants were removed, in the 

 latter part of February, just as the 

 buds w 7 ere beginning to start, the 

 galls averaged more than a half inch 

 in diameter. 



vSeedlings from one to six months 

 old are most susceptible to the dis- 

 ease. When trees of this age are 

 attacked the gall almost invariably 

 appears along the side of the main 

 root a few inches below the surface 

 or in the region of the crown. With 

 more mature trees the root-galls 

 often develop at a greater depth, 

 but most frequently on lateral roots. 

 The crown is also commonly at- 

 tacked on large trees. 



Two or three days after a gall first becomes visible to the 

 naked eye it is a clear, white, translucent mass of soft succu- 

 lent tissue a millimeter or less in diameter and usually nearly 

 or quite spherical in shape. It is most frequently attached to 

 the root by a narrow neck one-half or one-fourth of the diameter 

 of the body of the gall. If it appears on the parts above ground 



Fig. ii.— Seedling almond one- 

 half natural size, showing a large 

 gall with small pustules of fresh, 

 hypertrophied tissue developing 

 on its surface. 



