PSALLIOTA CAMPESTRIS 399 



which the fungus plant is unable to alter. So far as the fungus is 

 concerned, it may be beset with irregularly disposed mechanical 

 obstacles, it may be divided into moister and drier spots, it may 

 harbour lurking enemies, or be crushed down locally by the feet of 

 herbivorous animals. The mycelium, on arriving at the surface 

 of the substratum, gives rise to a considerable number of rudi- 

 mentary fruit-bodies which at first are all alike ; but very soon a 

 few, which occupy the most favourable situations for further growth, 

 draw to themselves the nutriment available in the mycelial strands 

 and thus rapidly increase in size. Most of the other rudiments 

 not so favoured cease to draw nutriment to themselves and soon 

 wither. It is not unlikely that some of the protoplasm of the 

 rudiments which become aborted is passed back again into the 

 mycelium, so that it may not be wasted, but ultimately finds its 

 way into the favoured fruit-bodies which are destined to develop 

 to maturity and thus propagate the species. By forming a large 

 number of rudimentary fruit-bodies at relatively little expense 

 in material and energy, the mycelium, as it were, carries out 

 a reconnaissance of the nature of the substratum-surface and 

 finally produces its effective reproductive organs only at the most 

 favourable points. 



Effect of Dry Weather on Development. I think it probable 

 that, in nature, the rudimentary fruit-bodies, like those of Coprinus 

 niveus and certain other coprophilous fungi which I have actually 

 observed, often have their development interrupted by lack of 

 moisture. If during what may be called the mushroom season 

 the weather continues dry, as everybody knows, no mushrooms 

 appear. If, after such a dry spell, the weather breaks and heavy 

 rain descends for a day or two so that the pastures are soaked, then 

 large numbers of mushrooms make their appearance in the course 

 of a very few days. I am inclined to believe that, when events 

 happen in this way, the mushrooms are already present during 

 the dry weather in the form of rudiments at the surface of the 

 ground, but that their further development and final expansion 

 have been delayed by drought which has temporarily checked the 

 supply of constructive materials coming up from the mycelial 

 strands. If the fruit-bodies which appear after a rainy day in 



