428 Agricultural Experiment Station, Ithaca, N. Y. 



prominent of these elevations possess a light brown appearance 

 and a perfectly herbaceous consistence. . . A cross-section of 

 the gall shows an irregular fibrous mass. In the smallest swell- 

 ings on the most slender roots, there may be recognized a small 

 dead portion in the center, and it is also the case in large roots 

 that a properly made cut will show that the swelling originated 

 from an injury to the woody cylinder of the root during the first 

 year of its existence. The injury may consist of a small crack 

 which extends from the outside to the center of the root at the 

 time when the latter was small, or the root during its first year 

 may have been torn and thereupon a callus appeared over the 

 wounded surface and this callus eventually developed into a root- 

 gall. The manner in which the first cracks appear has not been 

 clearly shown, but certain indications lead to the belief that they 

 may be caused by extremes of expansion and contraction. There 

 may be frequently found wedge-shaped bodies of parenchymatous 

 tissue in the rings formed during the first and second years' 

 growth of the root. These bodies (which may have the power of 

 forming adventitious buds) must show fairly deep crevices by 

 the alternate expansion and contraction of the tissues. The cir- 

 cumstance that such parenchymatous wedges may also appear 

 upon uninjured roots leads to the conclusion that the root-gall 

 may also arise without injury to the roots, but this is always a 

 more rare case. . . . 



" I therefore consider the root-gall as a swelling which ap- 

 pears either upon the body of the root, or at the crown, but which 

 is not caused by the action of any parasite. In the decayed sur- 

 face tissues of the galls, many organisms may be found; but in 

 the sound tissues I have been unable to discover any parasite. 

 I have also looked in vain for a form of Plasmodium. They ap- 

 pear to be caused merely by an abnormal flow of sap. Instead of 

 the uninterrupted return, to the ends of the roots, of the sap 

 which has been modified by the stems above ground, it finds a 

 constriction. This may be due to an injuiy of the root, or to its 

 having been bent at an acute angle. In such places the accumu- 

 lation of nourishing sap leads to the excessive growth which 



