108 INTRODUCTION TO THE STUDY OF FUNGI 



known, which attack various plants, and some unfortunate 

 hosts are the victims of two or three distinct species, all of 

 which appear to defy the ingenuity of man to eradicate them. 

 Equally disastrous in their effects, and persistent in their 

 attacks, are the '' rotting moulds," or Peronosporaceae, of which 

 the potato disease is one form, the American vine disease 

 another, besides many other species which are only of less im- 

 portance because the plants they attack are less extensively 

 cultivated, and less associated with the supplies of human food. 

 No one who has had experience of any of these pests amongst 

 his lettuces, onions, tomatoes, or in his clover field, would 

 estimate lightly their powers of destruction. The Urysiphei 

 also are a family of external parasites, the copious mycelium 

 of which take possession of living leaves, and destroy by 

 suffocation, closing and obstructing the air passages, and are 

 thus conspicuously destructive. Those parasitic Fungi, of which 

 a considerable number are now known, which establish them- 

 selves upon the bodies of living insects, and by the penetration 

 of the mycelium absorb all the tissues, soon cause death, and 

 then, in most cases, an external fertile manifestation of the 

 parasite takes place. In like manner the aquatic moulds of 

 the family Saprolegnieae, of which the moving cause of salmon 

 disease is an example, take possession of fishes and batrachians, 

 and carry on the work of destruction. There are also amongst 

 imperfect Fungi many entire genera which attack living plants 

 and ensure their quick destruction. 



Assuming that the power and influence of the Schizomycetes 

 are not exaggerated, what an agency for destruction must we 

 recognise in the bacterial Fungi, now so -wflaTy credited with 

 being the cause of many of the most destructive epidemic 

 diseases which affect the human subject, as well as inferior 

 animals ! If we only admit those which are proven beyond 

 dispute, it is scarcely possible to estimate the full extent of 

 the marvellous power possessed by organisms so minute in 

 the destruction of animal, and probably also of vegetable, life. 

 And so, as we walk through autumnal woods, we see vegetable 

 matter all around us in a state of decay, with Fungi living and 

 thriving upon it at the expense of the dissolving tissues, appro- 

 priating the changed elements of a previous vegetable life to 



