CHAPTER VII.— PLANT DISEASES. 



Crown Gall ob Hoot Gall. Fig. 17. 



This tli.sease causes galls to ajipear on the roots of various trees anil 

 shrubs. On fruit trees it coniinouly forms siilierieal swellings of various 

 sizes, occasionally as large as a walnut. These globular bodies have usually 

 a peculiar warty surface. They should not be confused with the galls formed 

 by W'Oolly aphis, which, moreover, are smaller and usually oval or irregular. 

 Besides, in aijhis galls some of the "wool" is usually to be found. 



It frequently haiipens that when the roots are affected with this disease 

 the secondary roots are abnormally al)undant and often somewhat spongy in 

 texture. 



Particular attention is called to this disease, because a gnod many nursery 

 trees have been sold in the Xorth-West with the roots altected by it. A safer 

 rule is to reject all trees diseased with the galls, even if the latter have been 

 removed. We have found that they are sure to ai)pear again. 



No remedy is known, and, as the disease ai>pears to be contagious, every 

 effort should lie made to jirevent the sale of nursery stock affected b.v it. 



Prof. J. W. Tnumey has recently discovered in Arizona that tlie crown 

 gall of the almond is caused by a slime mould which he names Dcntlniiihiiyiii 



I have been unable tii discover tliis or any simil.-ir organism in the galls 

 on apple roots. — V. H. D< imrtiniiil of A<jiiciilttirc. BuUrlin l.'i.l — I'iiirr. 



.\pplc Crown iJall on grafted tree. Hairy Root Disease on graftod apph' trc>o. 



(Fi(i. 17.) — Uull. 'JO, U. H. Department 0/ Agriculture. 



