CHAPTER VI 

 THE FUNGI : ARCHIMYCETES AND PHYCOMYCETES 



The Fungi are generally included as the second group of the phylum 

 Thallophyta. Some authorities, as we have already indicated, regard the 

 Fungi as a group of organisms of independent origin which cannot be 

 correctly included in a natural classification of plants, since, they argue, 

 Fungi are not plants at all. To follow such an argument to its limit it would 

 be necessary to postulate not two but three kingdoms, Plants, Animals and 

 Fungi. It is outside the scope of this book to discuss the relative merits of 

 these two views, and though there is much to be said in favour of the latter 

 we shall, for the sake of simplicity of treatment, regard the Fungi as members 

 of the Thallophyta. 



Whatever may be their correct systematic position the Fungi are a very 

 large and important group. There are something like 37,500 species definitely 

 known, and probably about three times that number in existence. About 

 9,000 species are known from Britain. Two of the largest orders are the 

 Urediniales and the Agaricales which include more than 4,000 species apiece. 



Fungi may be readily separated from green plants by the absence of 

 chlorophyll, and, since they do not feed holozoically, they must of necessity 

 live either as parasites on other organisms or as saprophytes on organic 

 compounds. The mode of nutrition exhibited by the Fungi varies to some 

 extent, but, in general, they make use of carbohydrates, amino-acids and 

 other organic substances. They also absorb nitrates, ammonia, phosphates 

 and sulphates. Such metals as Sodium, Calcium and ^Magnesium do not 

 appear necessary for their metabolism, though they may be essential to 

 higher plants. Some Fungi, however, appear to require traces of some of 

 the heavy metals such as Zinc, which are not generally necessary. 



With few exceptions all Fungi can live as saprophytes on nutrient media 

 composed of soluble organic substances, and it is in this way that many 

 hundreds of cultures are kept in laboratories for study. In fact many Fungi 

 which in nature appear to live exclusively as parasites are able to grow 

 saprophytically under cultural conditions. This plasticity of Fungi is one of 

 their most important features, coupled with a faculty for changing their 

 appearance to a considerable extent according to the composition of their 

 food. Many Fungi exhibit pleomorphism, that is, the power of assuming 

 various shapes not only in culture but also under natural conditions, a fact 

 which has greatly complicated their systematic study. 



In all but the simplest groups the vegetative thallus consists of a web of 

 filaments termed hyphae which together make up the body or mycelium. 

 This mycelium may either develop on or in the substrate, in the case of 

 saprophytes, or inside or on the surface of the host in the case of parasites. 



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