252 NEBRASKA STATE HORTICULTURAL SOCIETY. 



THE APPEARANCE OF CROWN GALL, 



There is practical unanimity upon this point among the 

 various authorities. The galls or nodules are usually found at 

 the crown of the root, although they are also, but less frequently 

 found upon the minor roots. Their size is variable. Starting 

 as a mere speck, they gradually increase in size until they 

 become as large as walnuts, sometimes as large as apples, and 

 sometimes even larger. They are soft, spongy, and granular, 

 and, although whitish in color when young, they gradually 

 assume the same color as the roots. The galls are usually 

 annual in growth, that is, they begin their growth in the spring 

 and become mature in the fall. Around the galls a mass of 

 fine, fibrous roots usually start out. They are not to be con- 

 fused with the galls produced by the wooly aphis. The latter 

 galls are small, hard, and are mere swellings of the roots, while 

 the former are large, spongy, and are more in the form of 

 excrescences. 



WHAT CAUSES CROWN GALL. 



This question has never been settled. There are a variety of 

 theories concerning it, but none have been generally accepted 

 by the botanists of the world. Sorauer, the celebrated German 

 botanist, gives it as his belief that the disease is caused by an 

 injury to the root, such as bending or breaking it in the process 

 of transplanting. Since the galls were first noticed on stock 

 coming from irrigated districts it was concluded that irrigation 

 was the cause. But this idea was abandoned when cases of 

 crown gall were found in compartively dry places, where irri- 

 gation had never been practiced. The galls are frequently 

 found at the place of union of the stock and scion in root-grafted 

 trees, and it was thought at one time that grafting was the 

 cause of crown gall, but since the galls are common upon seed- 

 lings which have never been touched by a knife, grafting can- 

 not be regarded as the cause of the disease, although it may 

 provide for the easy entrance of the disease into the plant. The 

 latest and most elaborate opinion as to the cause of crown 

 gall is that of Professor J. W. Toumey of Arizona. As a result 

 of a course of careful experimentation he decided it to be due 

 to a certain organism very low in the scale of life, belonging to 



