8 BULLETIN 1347, U. S. DEPARTMENT OF AGRICULTURE 
sheaths are held fast to the culm by the dense growth of interwoven 
mycelium. 
Plants which are attacked during the middle of the summer grow- 
ing period usually remain erect and stiff until cut down at harvest. 
However, cases have been noted where such plants break over at the 
base. When an attempt is made to pull the diseased plants out of 
, the soil they frequently break off at the soil line, and when this break- 
ing does not occur it will be found frequently that the root system is 
badly rotted. 
When plants become infected or react to previous infection after 
the heading stage, the whole plant becomes bleached, and a white- 
head condition results. Such heads produce no grain or grain which 
is of light weight, depending on the stage of seed development at 
the time the plant succumbs to the attack by the fungus. 
It is not uncommon to find plants showing only a mild root or 
culm infection without any apparent injury to the aboveground 
parts. In such cases the bases of the culms may show only a black- 
ening, with no indication of tissue disintegration, and the roots will 
have but few lesions. It also is common upon removing dead plants 
from the soil to discover that their culms are perfectly clean and the 
root system completely rotted. Likewise there are cases where death 
is apparently due entirely to the rotting of the culms and crowns. 
In many cases some of the culms of a plant are killed and the others 
unaffected. | 
The writer has observed that a small percentage of experimental 
plants infected with Ophiobolus graminis tends to develop more of a 
brown than a black discoloration at the bases of the culms, a condi- 
tion resembling the browning produced by Helminthosporium sati- 
vum and by Grbberella saubinetu. This browning, however, is 
seldom produced by O. graminis without some development of a 
black or dark-brown mycelial weft or plate on the browned parts 
of the plant, which plate is absent from the bases of plants attacked 
by H. sativum or G. saubinetii. In this connection, however, the 
writer does not wish to imply that O. graminis is the only wheat 
parasite that produces a mycelial plate. 
CAUSE OF THE DISEASE 
Take-all is caused by a sac fungus, which has been generally 
designated by the name Ophiobolus graminis Sacc. ever since 
pathologists recognized that this parasite is associated with this 
disease. It now appears, however, that certain workers doubt the 
validity of this binomial, and it may be well to present the available 
evidence bearing on the subject. 
In going over the literature it appears that Berlese (7, pp. 119- 
120) made a study of certain species of Ophiobolus and reported 
| that there are certain cases of synonymy. He compared the type 
specimens of Ophiobolus eucryptus (Berk. and Br.) Sacc., O. cariceti 
(Berk. and Br.) Sacc., and O. graminis Sacc. and found that they 
agreed. On the basis of these comparisons Berlese held that inas- 
much as the name O. eucryptus antedated the other two by a number 
of years the latter names become invalid. Strangely enough, how- 
ever, Berlese’s interpretation was never generally accepted, and 
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