4 PLANT DISEASES 



FUNGI 



A terse definition of the nature of a fungus is not 

 possible. Toadstool, mushroom, rust, mildew, and mould 

 are popular names for different groups of fungi, of which 

 we have above four thousand species in Britain alone, 

 whereas the Fungus-flora of the world includes above 

 fifty thousand species. 



Accepting the fact that fungi are true plants, there is 

 one important feature in their life-history which must be 

 clearly understood, in order to realise why so many fungi 

 prey upon and kill plants belonging to other groups of 

 the Vegetable Kingdom. This feature relates to nutrition. 

 It is well known that flowering plants derive one portion 

 of their food from the soil, and another portion from the 

 air. These substances are inorganic, that is, they are not 

 the direct products of a living body, but under the 

 influence of the chlorophyll or green colouring matter 

 present in leaves these substances become converted into 

 plant food, an organic substance, the direct result of work 

 done by the living green leaves. 



Now, fungi are entirely destitute of chlorophyll, hence 

 they cannot assimilate inorganic food, but require organic 

 food, and this they obtain by feeding on the bodies of 

 other plants. For this reason we always find fungi follow- 

 ing in the wake of flowering plants. Some few fungi 

 obtain their food from animal bodies, living or dead. 

 The different methods adopted for securing this organic 

 food enable us to divide the fungi into two groups. 



I. Saprophytes. — Those fungi are termed saprophytes 

 that live on dead organic matter, as dead wood, heaps Oi 

 dead leaves, etc. ; and as such are not injurious to living 



