32 CAUSE AND NATURE OF CROWN-GALL 



the seedlings, although the worms in the decayed wood had in- 

 creased in number to a marked degree. 



The other nematode observed was the common gall-forming 

 species, Heterodera radicicola. In a few instances the galls 

 formed by this worm and the crown-gall were associated to- 

 gether in the same specimen. The galls, however, are very 

 distinct and cannot ordinarily be mistaken for each other. In 

 Fig. 10 the galls formed by this nematode are shown on the 

 roots of an almond seedling. A description of this worm and 

 its effect upon the peach has been published by Atkinson.''' 



PLANTS SUBJECT TO CROWN-GALL. 



Although at present I am unable to state that all plants upon 

 which these characteristic galls appear are of identical origin, 

 it is reasonable to expect that if not they are caused by nearly 

 related parasites. No matter upon what plants the galls ap- 

 pear, they are always readily distinguished from all other forms 

 of hypertrophied tissue. 



Personally I have found the crown-gall upon the peach, apri- 

 cot, almond, prune, plum, apple, pear, English walnut, and 

 grape, and have examined specimens from Arizona, California, 

 New Mexico, and Utah. Further east it is reported as infest- 

 ing the raspberry, blackberry, cherry, and poplar, as well as 

 the plants named above. I am informed by W. W. Ashe that 

 it is indigenous in South Carolina on the chestnut, and that it 

 frequently kills the trees. 



Although I have repeatedly succeeded in communicating the 

 disease on the almond to the apricot and peach, I have not suc- 

 ceeded in communicating it to the English walnut, apple, and 

 grape, either by soil inoculation or by incisions through the 

 bark. Halsted's 30 experiments indicate that the galls on the 

 raspberry have no power to induce the formation of galls on 

 the peach. On the other hand, Selby :iI concludes from his ex- 

 periments that the disease can be communicated from the rasp- 

 berry to the peach. The question whether the galls found on 



29 Bull. Ala. Agr'l Exp. Sta., 9 (1889). 

 30 Rept. Bot. Dept. N.J. Agr'l Exp. Sta. 1896, 414. 

 ' Bull. Ohio Agr'l Exp Sta., 92, 214. 



