SOFT ROT OF CARROT: NON-NUTRITIONAL ENVIRONMENT 251 



Why does 5 per cent grape-sugar retard or inhibit growth? 

 Why does it ear y kill off the cultures grown in media containing 

 it? 



For the disease : Signs. — Write a description of the signs 

 of this disease drawn from your own inoculations on carrots and 

 other vegetables. How many hours from inoculation to the 

 first appearance of the soft rot? Study the progress of the 

 rot as related to: (1) copious vs. sparing inocu ation; (2) moist 

 vs. dry air; (3) cool vs. warm air; and (4) flabby vs. turgid tissues. 

 At what cool temperature does the rot cease? Above what tem- 

 perature does it cease? Compare this organism with No. IV, 

 especially on raw potato, and with No. VII. 



Submit photographs or good drawings or both. Remember 

 you cannot have too many striking and conclusive illustrations 

 of the various diseases. 



Histology. — Fix, embed, section and stain early stages and 

 late stages of the rot on various plants to determine location and 

 action of the organism. Are the cells invaded or is the action 

 of the organism entirely extra-cellular? Do not conclude too 

 hastily. How are the middle lamellae destroyed, i.e., by tear- 

 ing or by solvent action? What is the composition of this mid- 

 dle part of the cell-wall? Is cellulose destroyed? How are 

 the bacterial cavities formed? Are the cells killed in advance 

 of the bacterial invasion ? Does the water-soaked area surround- 

 ing a bacterial nidus stain the same in sections as the sound 

 area just beyond (see Fig. 172 at x)? Under the microscope 

 unstained, does it look the same? What differences in the cell- 

 wall? in the cell contents? In the attacked parts just previ- 

 ous to disintegration are the cell- walls swollen? Make good 

 permanent preparations showing various stages of the tissue- 

 disintegration. 



Variability. — There appears to be considerable more resis- 

 tance in some varieties of the attacked species than in others. 

 Is this accidental or inherent? Why are green tomato fruits 

 more subject than ripe ones? Why is the core of the carrot 

 rotted sooner than the outer part? Why are young (seedling) 

 carrots exempt? Are they, really? Why are the green parts 

 of susceptible plants not more generally attacked? Read what 



