THE DJSKASI-;. 



compacted, al)oi'ted, and enlarged into a flesh)- edible mass, might well l)e regarded 

 as a diseased condition, but it is not so regarded for the purposes of this book. 

 On the contrar\-, a soft rot of the caulifl(j\ver head is regarded as a disease. l!acterial 

 diseases of plants usually in\'olve both functional and structural changes. 



Inasmuch as the word " S)'mptoms " has a subjective as well as an objective 

 connotation in medical terminology, the writer has preferred to substitute the word 

 "signs" for those objective characters which ser\-e to distinguish one plant disease 

 from another. 





r-iM 





i'-HPir^d. 



The student will, naturally, first turn his attention to a careful study of the 

 disease. Under this head should be considei'ed : (i) Previous literature ; (2) 

 Geographical distribution ; (3) Signs of the disease ; (4) Pathological histolog}- ; 

 (5) Direct-infection experiments. 



■ Fig. 2. — Cross-section of a raw carrot, showing wedging apart of parenchyma cells by Bacillus 

 carotoi'oriis Jones; from paraffin-infiltrated material The carrot was fixed in strong alcohol 72 

 honrs after placing on its cut surface one loop of a fluid culture. The inoculation was made in the 

 middle of a cross-section of the whole root, i om. thick, placed in a sterile Petri dish. The surface 

 of the root was sterilized in mercuric chloride water. This section was made several millimeters 

 below the inoculated surface, A small portion of it at X is shown more highly magnified in fig. 3. 

 This section was stained with carbol-fuchsin and bleached in 50 per cent alcohol. Drawn under Zeiss 

 16 mm. apochromatic objective with No. 4 compensaiting ocular and the Abbe camera. 



