91 
A Make pRawincs to show symptoms exhibited in the older stems and 
Ops. 
A variety of symptoms have been described for the tubers of affected 
plants. In the specimens or photographs provided, oBSERVE:— 
12. The large number of small potatoes from a diseased hill as 
compared with those from a healthy hill. Lesions on the tuber-stolons 
cut the young potatoes off before they can mature. The plant is thus 
stimulated to a production of more tubers which in turn are likewise pre- 
vented from reaching mature size. (Maine Bul. 230, fig. 69.) Draw. 
13. That tubers themselves may be affected, showing a russeting 
or even deep cracking of the surface. Cankers or pits in the tubers are 
held by some investigators to be frequent symptoms of this disease. 
(Maine Bul. 230, fig. 72-73.) praw. 
The most striking and certain diagnostic sign of this disease is the 
presence on tubers of the sclerotia of the pathogene. Examine the tubers 
provided. OBSERVE :— 
14. The numerous, dark-brown or black sclerotia scattered over 
the surface of the tuber. 
15. Their irregular size and shape. 
16. That on attempting to scrape them off, they cling very 
tightly, but when they come away it is evident that they are entirely 
superficial. DRAW a tuber to show the character and distribution of the 
sclerotia. These sclerotia are not usually associated with lesions on the 
tuber and are exceedingly common on potato-tubers, even from apparently 
healthy plants. 
Sclerotia may appear on the stems or roots as well as on the tubers. 
(See illustration specimens.) 
On the carnation. This is probably the most serious carnation disease 
with which florists have to contend. Both cuttings and older plants 
are affected. Cuttings are attacked below the surface of the soil and rot 
or damp-off like seedlings. 
Examine the specimens of diseased plants provided. OBSERVE :— 
17. The silvery gray color of the foliage as compared with the 
grey-green of the healthy plants. 
18. The erect and withered habit of the diseased plants. 
19. The soft and rotted cortex of the stem just at, or above, the 
surface of the soil. It comes away very readily from the wood. 
20. In the crevices of the bark, the dark-brown sclerotia of the 
pathogene; not always easily discovered. 
DRAW to bring out the contrast, so far as you can, between diseased and 
healthy plants. 
ETIOLOGY 
The cause of this disease, so cosmopolitan both as to hosts and range, 
is the basidiomycetous fungus, Corticiwm vagum Berkley and Curtis, 
long known in its mycelial form as the sterile fungus, Rhizoctonia Solant 
Kahn. 
Life-history. This pathogene presents some unusual features in its 
life-history. True conidial bodies are wanting. Sexual spores, the 
basidiospores, are formed, but apparently with no regularity and only 
under certain very favorable conditions. Sclerotia of a very simple type 
are produced in great abundance and doubtless are the only structures 
which serve to carry the pathogene over from one season to the next. 
