242 FLEAS, FLUKES AND CUCKOOS 



Fungi 



Fungi are plants without chlorophyll which live as saprophytes, 

 parasites, commensals or symbionts. All the species attacking birds and 

 mammals are facultative parasites which pass from a saprophytic mode 

 of life because conditions happen to favour the change. Fungi 

 attacking other plants are often obligatory parasites and strictly host 

 specific. 



The parasitic fungi of birds are microscopic organisms and the 

 reader will be disappointed if he expects to see a robin with a large 

 mushroom sprouting under its wings or from between its toes. The 

 host's reactions to viruses and bacteria are visible to the naked eye and 

 one can see pockmarks and boils. Similarly, fungi are responsible for 

 obvious lesions, such as the red patches of ringworm, but the causative 

 organism has to be sought and examined with the aid of a microscope. 

 The general appearance and colour of colonies of fungi grown in the 

 laboratory are however of great importance for the purpose of identifica- 

 tion. 



A typical parasitic fungus consists of filamentous branching threads 

 or hyphae, with a tough chitinous outer covering, collectively forming a 

 mycelium, which ramify through the tissues of the host. These fila- 

 ments absorb the decaying substances or solutions in which they are 

 immersed and can also secrete various enzymes which assist them in the 

 process of decomposing organic matter. Fungi reproduce either by a 

 sexual or asexual process. They give rise to spores which are extremely 

 long lived or resistant and can germinate after a resting period of 20 

 years or more. 



In many respects fungi resemble bacteria. In some forms the my- 

 celium breaks down and forms chains of cells, or fragments into separate 

 cells, and in these stages it is virtually impossible to distinguish them 

 from bacteria. Conversely in some classifications, certain bacteria are 

 placed among the fungi and the mycelium is described as "rudimentary 

 or absent." 



Diseases which result from attacks by fungus are known collectively 

 as the mycoses. A great variety parasitises man and in his Precis de 

 Parasitologie Brumpt considers them sufficiently important to assign 

 them 429 pages out of a total of 2,064. Some of these species also 

 attack birds. Favus, which is a chronic mycosis of the skin, is produced 

 by various members of the genus Achorion. Thrush, a mycosis of the 



