i] SAPROPHYTISM 7 



SAPRQPH1 TISM 



According to our present knowledge the large majority of fungi are 

 saprophytic; a considerable proportion of forms in each of the great groups 

 and especially a very large number of the Basidiomycetes obtain their 

 nutrition in this way. 



On Wood. Ascomycctes and Basidiomycetes arc important agents in 

 the breaking up of wood; their hyphae absorb the starch and protoplasm 

 of the unaltered cells of the wood and medullary rays and penetrate into the 

 fibres, vessels and tracheids, either passing through the pits and especially 

 the bordered pits, or penetrating the walls. They act upon the walls so that 

 these become delignified and give characteristic cellulose reactions and the 

 middle lamella is dissolved. The enzyme responsible for this change was 

 first isolated by Czapek in the case of Merulius lacrymans, the fungus of 

 dry rot. Its action seems to spread in a plane parallel to the surface of the 

 wall either from the pits, which thus become much enlarged, or from the 

 delicate passages left by the protoplasmic connections which originally 

 traversed the walls of the young wood elements. The whole mass of wood 

 loses weight and may reach the easily broken and almost powdery condition 

 known as touch-wood. In this way considerable damage may be done to 

 timbers (dry rot, Merulius lacrymans), paving blocks (Leutiuus Icpidctts), etc., 

 but also considerable advantage may ensue from the restoration to the soil 

 of the material of fallen tree trunks, twigs and branches. 



The part played by the higher fungi is here specially important as almost 

 the only other agents of destruction of lignified tissues seem to be certain 

 molluscs and Crustacea which act by boring into the wood. 



On Soil. Yeasts and filamentous fungi arc abundant in woodland soils 

 and they are also of frequent occurrence in cultivated soil; the microscopic 

 forms show a remarkable similarity in different localities; even in Europe and 

 America the same genera and often the same species are obtained ; in culture 

 there is a regular succession of forms, first the Mucoraceae, then Penicilliant 

 and Eurotium and later the black and brown Hyphomycetes. A large 

 number of Basidiomycetes also develop in the soil. 



The fungi of the soil utilize the sugar, starch, pectose and hcmi-cellulose 

 which are returned to the ground in dead plants and plant org ins, and, in 

 common with certain bacteria, they act upon cellulose, breaking it up into 

 soluble substances and humus. In several cases evidence has been brought 

 forward that some of these fungi are capable of assimilating free nitrogen 

 but negative results have also been very common. 



The activity of these fungi is well exemplified by the "fairy-rings" of 

 dark green grass often seen in poor pastures. The soil just outside the ring 

 is rich in the mycelium of one or two common fungi; few hyphae are found 



