40 DISEASES OF CROP-PLANTS 



The Protobasidii include the most important single order of 

 plant parasites, the Uredinales or rust fungi (see p. 17). The 

 relation to Basidiomycetes is shown in the germination of the 

 teliospores, formed direct from the mycelium, which in similar 

 fashion to the chlamydospores of the smuts typically produce in 

 germination a filament divided towards its free end into four 

 cells, each of which produces a sporidium, regarded as a basidio- 

 spore. 



The Eubasidii contain, among other types, the mushrooms, 

 toadstools, bracket-fungi and other large forms which are the 

 most conspicuous and familiar of fungi. The number of plant 

 parasites among them is relatively small. 



Some of the Hypochnacese form a thin webby covering on 

 living leaves, and have been held to be associated with thread 

 blights. 



The Thelephoraceae form a thin, leathery, membranous, or 

 web-like covering on the substratum, often in extensive sheets 

 or patches. The genus Corticium contains the fungi of the West 

 Indian thread blights and of pink disease ; Odontia spp. are 

 associated with root disease of sugar-cane ; the Septobasidiums 

 are believed to live at the expense of scale insects (see Grey 

 Blight of Limes). 



The Polyporaceae, many of which have bracket-like fructifica- 

 tions, take a large part in the destruction of dead wood, and in 

 some cases extend this mode of life to the wood of living trees if 

 they can obtain access through wounds, dead branches, or 

 debilitated parts. They are distinguished by the arrangement 

 of the hymenium as a lining to a system of pores, which may be 

 shallow, or deep and tubular. The fruiting bodies are often 

 large, and may be soft and fugitive or leathery to woody and 

 persistent. 



The Agaricaceae are the gill-fungi, so called from the extension 

 of the hymenium over a series of thin flat plates of tissue, as in 

 the mushroom. Usually the fructifications consist of a roundish 

 cap (pileus), bearing the gills on its under side and supported by a 

 stalk (stipe), or attached by a part of its margin. Very few of 

 the Agaricaccce are parasites, but Marasmius contains injurious 

 species, one of which is the cause of a serious disease of cacao, 

 while others are associated with root diseases of sugar-cane and 

 banana. Schizophyllum is a common saprophyte which some- 

 times appears on failing sugar-cane. 



Class IV. Fungi Imperfecti. 



The exceedingly numerous groups and species of fungi 

 collected for the sake of reference in this class are not imperfect 

 in their powers of maintaining themselves, but have not been 

 found to possess any character which enables them to be fitted 

 into the classes already described. A very large number of 

 important plant parasites are found among them. 



