226 DISEASES OF CULTIVATED PLANTS 



colour, and produces the winter form of fruit, as this is what 

 sets up the infection in the spring. 



Prillieux, Malad. des Plantes Agric., 2, p. 96 (1897). 

 Tulasne, Fung. Sel. Carp., 3, p. 24. 



OPHIOBOLTJS (RKiss.) 



Perithecia scattered, submembranaceous, asci cylindrical, 

 typically 8-spored ; spores needle-shaped, septate or guttulate, 

 hyaline. 



Very minute fungi, growing on culms, stems, etc. 



1 Take-all ' and ' White-heads ' in wheat (Fig. along with 

 Gibellina cerealis, see p. 242). These names, according to 

 M'Alpine, are used in Australia to describe the serious inroads 

 made by a fungus called Ophiobolus graminis (Sacc.) on the 

 wheat crop during different stages of growth. The disease 

 is equally well known in some parts of Europe, and is called 

 'Maladie du pied,"Pietin du Ble,' 'Foot-rot,' ' Black-leg,' etc. 

 In England it is known as ' Straw blight.' The Australian 

 names are very expressive, and are used here. The ' take- 

 all' symptoms are the presence of stripes or patches where the 

 wheat plants appear to have been checked in their growth, 

 dying off while young, so that nothing remains but dead, 

 shrivelled plants. The 'white-head' condition does not 

 show until the ears are fully formed, but remain ' deaf/ the 

 grain not developing, and on examination not only are the 

 ears found to be bleached and dead, but also the entire 

 plant down to the ground. These two marked symptoms 

 were at one time considered as distinct diseases ; both, how- 

 ever, are now known to be caused by the same fungus, and 

 careful examination shows that wheat plants succumb at all 

 stages of development. Broadly speaking, when the plants 

 are attacked when quite young, the ' take-all ' stage predomi- 

 nates, whereas when the plants are infected at a much later 

 stage, the ' white-head ' appearance predominates. The root 

 and base of the culm are the parts attacked. 



The vegetative portion of the mycelium penetrates the 

 tissues of the lower internodes of the culm and of the root, 

 which become brown and dead. A brown superficial my- 

 celium is also formed on the surface of the culm and on 

 the inside of the leaf-sheaths, which becomes compact, 



