26 
SKETCH to show field symptoms. (See demonstration material.) 
14. Diseased rhizomes if available. Make a similar compara- 
tive study and pRaw. 
ETIOLOGY 
The pathogene responsible for this soft rot in such a variety of hosts 
is Bacillus caratovorus Jones. It was first described from carrots. 
Life-history. This organism doubtless hibernates in host-debris or 
in the soil itself. ; 
The Primary Cycle is initiated when the particular host concerned 
is in the best stage of its development for the attack. Succulent tissue 
is a requisite. The iris is usually affected very early in the spring while 
carrots, turnips, cabbage and cauliflower are first attacked late in summer 
or autumn. . 
Pathogenesis. The source of the primary inoculum is doubtless the 
soil or rotting host-tissue in the soil. The bacteria are carried to the roots 
or rhizomes by snails, insects and probably flowing water. They can enter 
apparently only through wounds. Once within susceptible tissue with 
abundant moisture present they multiply rapidly and -cause the disintegra- 
tion of the parenchyma. 
Remove a bit of the rotten tissue to a drop of water on a slide, cover 
and examine for the bacteria. OBSERVE :— 
15. Their abundance, and relation to the cells of the host. 
Are they within or without the cells; motile or non-motile; single or 
in threads? Are spores present? DRAW. 
16. The photomicrograph showing the flagellate stage of the 
pathogene. How many flagella has each bacillus and how are they 
arranged? DRAW. 
Saprogenesis. This organism is doubtless able to multiply in 
host-debris in the soil so that virulent active inoculum is always present 
where the pathogene has flourished the previous season. It grows readily 
on culture-media. 
Examine the pure culture provided. skETCH and DESCRIBE:— 
17. A typical colony as to form, color, consistency and odor. 
Make a mount from one of the colonies and compare the bacteria 
with those from the tissues as to the points indicated in No. 15. 
Secondary Cycles are initiated from, and develop in the same man- 
ner as the primary cycles. 
Pathological Histology. Make several thin longisections through a 
small piece of the healthy organ (root, leaf-base or rhizome). IDENTIFY :— 
18. The various tissues present. The cell-contents and organs 
in each. Make a pRAWING detailing a portion of the section, a few cells 
wide, from epidermis toward the center. Show with especial care the inter- 
cellular spaces and contiguous walls of the cells. 
Remove the epidermis from over the soft portion of a lesion. With a 
needle or point of a scalpel remove a bit of the rotten tissue to a drop of 
water on a slide, cover and gently press on the cover. Study and oBSERVE:— 
19. That the individual cells are separated from each other 
but are stillintact. Identify the kinds of cells seen with those in the healthy 
leaf. Compare their shape with corresponding healthy cells. 
20. The disorganized and plasmolized character of their con- 
tents. What organs of the cell can still be identified? 
