Bean Anthracnose 119 



hours some of these appressoria themselves send out a slender germ tube, 

 at the end of which in most cases another appressorium is formed. After 

 nine days about 50 per cent of the spores in this experiment had germi- 

 nated but had not proceeded much beyond the production of appressoria. 

 A number of spores had the appearance of being empty, and other 

 peculiarities were noticed to which no importance could be attached. 



Frank (1883 b: 513-515) describes the germination of the spore and 

 the formation of appressoria, he being the first to apply the name to these 

 bodies. These appressoria, Frank says, come to have a thick, irregular, 

 dark purple membrane. They are produced abundantly when spores 

 are germinated on the surface of bean or cucumber tissue, but seldom 

 occur when germination takes place in water on a glass plate. Instead, 

 long, thin, germ tubes are formed, at the end of which a small appressorium 

 may appear, or the spore may produce another spore or sporidium attached 

 directly to the spore or to a short tube. Frank says the appressoria do 

 not germinate unless they are in contact with the host. He thinks their 

 production is stimulated by the quality of the substratum, and suggests 

 that their function is to prepare the fungus for penetration into its host 

 plant. 



Appressoria are produced by other Gloeosporia of the Glomerella 

 type, and their significance has been discussed by other writers. Halsted 

 (1893 a: 305) suggests that they may be formed as a protective body 

 to tide the germinating spore over unfavorable periods. He says that, 

 while the appressorium is often a single cell, it may become an aggregation 

 of thick-walled cells like a sclerotium. He thinks the appressoria may be 

 of taxonomic value. Stoneman (1898:113) does not find them to occur 

 as a constant character, but thinks they may be forced in certain species 

 by lack of nourishment. Hasselbring (1906:142), from studies of Gloeo- 

 sporium frudigenum Berk., believes them to be adhesion organs during 

 early stages of infection, and thinks they are formed as a result of contact 

 stimuli of the germ tube but lose this power of reacting in nutrient media. 

 He calls attention to the presence of a germ pore in the flattened side, 

 through which the germ tube protrudes during germination. He finds 

 the appressoria much more resistant to desiccation than the spores. 

 Edgerton (1910:21) finds appressoria produced in nutrient media, often 

 not in contact with the glass or any solid substance; and in this species, 

 Colktotrichum lindemutkianum, the " germ pore " is often lacking. 



