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THE DISEASE. 5 
compacted, aborted, and enlarged into a fleshy edible mass, might well be regarded 
as a diseased condition, but it is not so regarded for the purposes of this book. 
On the contrary, a soft rot of the cauliflower head is regarded as a disease. Bacterial 
diseases of plants usually involve both functional and structural changes. 
Inasmuch as the word “symptoms” 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 serve to distinguish one plant disease 
from another. 
The student will, naturally, first turn his attention to a careful study of the 
disease. Under this head should be considered: (1) Previous literature ; (2) 
Geographical distribution; (3) Signs of the disease ; (4) Pathological histology ; 
(5) Direct-infection experiments. ; 
* Fic. 2—Cross-section of a raw carrot, showing wedging apart of parenchyma cells by Bacillus 
carotovorus Jones; from paraffin-infiltrated material. The carrot was fixed in strong alcohol 72 
hours 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, 1 cm. 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 shawn more highly magnified in fig. 3. 
This section was stainedwith carbol-fuchsin and bleached in 50 per cent alcohol. Drawn under Zeiss 
16 mm, apochromatic objective with No. 4 compensating ocular and the Abbe camera. 
