CLASSIFICATION OF FUNGI 49 



the grasses. The fungus attacks the grass above the 

 ground, usually the upper part, and forms a white or 

 tan-coloured pod-like structure around the stem or 

 leaves, causing them to be strangled. The conidia 

 are similar to those of the powdery mildews. As the 

 growth approaches maturity numerous cavities, opening 

 to the outside, are formed. In these cavities are the 

 sacs containing the spores. This disease is common in 

 Malay and other tropical countries. 



Order 7. SPHAERIALES. This is one of the very 

 largest orders of fungi, and the species are the cause of 

 numerous plant diseases, although the great majority 

 are saprophytic. They range in habit from leaf parasites 

 to terrestrial forms, but agree in character of the repro- 

 ductive structures. The great majority grow on woody 

 or herbaceous stems, and with but few exceptions the 

 mycelium is in the substratum. The great majority 

 are inconspicuous. 



Species belonging to the genus Leptosphaeria (Fig. 

 30) produce leaf-spots which are irregularly distributed 

 over the surface, and usually vary in colour with their 

 age. When fully mature the perithecia are to be found 

 buried in the tissues of the leaf, and projecting slightly 

 above the surface. They are almost spherical, and 

 contain long, slender, clavate cylindrical asci (sacs), 

 within which are the spores. The spores are usually 

 colourless, becoming yellowish when old. The most 

 important tropical species of this genus is L. sacchari, 

 van Breda, of the sugar-cane (page 88). 



The genus Mycosphaerella (Fig. 31) also contains 

 many species which cause leaf-spot diseases. These 

 spots also vary in size and colour depending upon their 

 age. The conidia spores are formed very early in the 

 history of the spot, but the ascospore stage does not 

 appear until a much later period. M. fragariae, (Tul.) 

 Lindau, is the cause of a common leaf-spot disease of 

 the strawberry in the United States, and has in all 

 probability been introduced into the tropics. M. 

 stratiformans, Cobb, of the sugar-cane (see pp. 89, 112) 



E 



