512 BIOLOGY OF THE MICRO-ORGANISMS. 



solution of cellulose, also, has been frequently noticed as 

 a result of the penetration of mould fungi into the tissues 

 of plants, and is only explicable by the agency of 

 ferments. 



The parasitic existence of the mould fungi, in which 

 they take the necessary nutrient materials from the host 

 on which they grow, will be considered at greater length 

 further on. 



8 ' Other Conditions of Life of the Mould Fungi.- 



f actors. Increased and diminished atmospheric pressure, light 



and electricity, have not yet been exhaustively studied as 

 regards their influence on the growth of the mould fungi ; 

 in so far as existing observations enable us to draw con- 

 clusions on this subject, they appear to have no marked 

 effect. Nothing is known as regards either a disturbing 

 or favourable influence of movement of the nutrient mix- 

 ture; and with regard to a favourable or inhibitory 

 action of fermentation on the growth of the mould fungi 

 there can be no question whatever, for with the above- 

 mentioned exceptions they do not cause fermentation. 

 There remain, however, some conditions of life which 

 may influence the growth of the fungi, more espe- 

 cially temperature, and concurrent growth with other 

 fungi. 



Temperature. Temperature only requires consideration in so far as 

 it varies within medium limits. The extremes of cold 

 or heat will be considered among those conditions 

 which may cause the death of the fungi. In the case 

 of those temperatures which come into play under 

 normal conditions, the same points are of importance 

 as were mentioned with regard to the concentration 

 of the nutrient materials. In the case of the mould 

 fungi there exists an optimum of temperature at which 

 they grow most quickly and flourish best; but this 

 optimum differs according to the species of fungus, and 

 also according to the other conditions of life and nutri- 

 ment, in any given case. The optimum for penicillium 

 is quite different from that for aspergillus, and they both 

 differ from that of mucor. Penicillium glaucum appears 

 to grow best at a temperature of about 20 C.; it grows 



