40 DISEASES OF TREES 



FUNGI 



THE STRUCTURE AND LIFE-HISTORY OF FUNGI GENERALLY 



Every fungus consists of a mycelium and a sporophore. 

 The former takes in and elaborates the nutrient materials, and 

 discharges all vegetative functions, whereas the sporophores 

 produce the organs of reproduction, which may have a sexual or 

 an a-sexual origin, in the latter case being produced in a vegeta- 

 tive manner by division and abscission, a process analogous to the 

 formation of buds in the higher plants. The mycelium has its 

 first inception in a tubular outgrowth which is produced during 

 the germination of a fungal cell, and which by absorbing 

 water, and usually food-materials as well, forms what is called 

 a fungal filament, germ-tube, or " Hypha." The germ-tube is 

 characterised by apical growth, and by the formation of lateral 

 branches, whereby a system of fungal tubes (hyphse) is formed 

 which is constantly anastomosing, and which has erroneously 

 been compared to a stream with its tributaries and springs. 

 This comparison is not apt, because fungal hyphae are almost 

 uniform in diameter,* there being usually but little growth 

 in thickness of the oldest part of a system of filamentous 

 mycelia. 



In the case of some species, no partitions form in the fungal 

 filaments or hyphae, but as a rule transverse septa, which divide 

 the internal space into chambers, are formed a short distance 

 behind the apex. Such a hypha is said to be " septate." When 

 quite young its contents consist of protoplasm, which is usually 

 colourless, and only at some distance from the apex does a 

 granular appearance manifest itself, which is generally due to 

 the formation of fat globules. The cells of the mycelium are 

 frequently filled with large drops of fat, and this is especially the 

 case when the mycelium assumes a condition of inactivity, in 

 which it remains till growth is again resumed. The potato 

 tuber, by storing up reserve materials (in this case chiefly 

 starch), which are not utilized in the formation of new 



* [Nevertheless, as the author himself points out on the next page, the 

 hyphae developed later are often progressively finer and finer than those 

 first produced. This is strikingly obvious in the case of some moulds e.g., 

 Mucor. ED. 



