514 BIOLOGY OF THE MICRO-ORGANISMS. 



different classes of fungi is important, and must be 

 noted under various other circumstances. A similar 

 concurrence naturally occurs also among the species 

 of one and the same class ; in that case, however, 

 other factors come into play, and lead to one or 

 other species gaining the upper hand. Temperature 

 has a very marked influence ; if, for example, we 

 employ a nutrient medium at 15 C., in which the spores 

 of Aspergillus fumigatus and of penicillium have been 

 sown, only the latter fungi will develop well, and they 

 will grow to such an extent that growth of the aspergilli 

 cannot occur, although this would have taken place 

 had there been no penicillium spores in the material in 

 the first instance; and conversely, where both species 

 are sown together in a medium kept at 35 C. only the 

 aspergilli ultimately develop. Other nutrient conditions 

 also act in a similar manner, and hence the resulting 

 cultivation and also the presence of any given mould 

 fungus in nature does not rest alone on the various con- 

 ditions of life which are present, but also depends in a 

 very important manner on the other species of fungi 

 which may have reached the nutrient soil at the same 

 time and may be growing in concurrence with it. 

 Conditions of 4. Conditions of Spore Formation and Spore Germina- 

 *pore forma- ^ 0?l< j n the case of the mould fungi, the formation of 

 spores is such an essential part of the life of the fungus 

 that we cannot regard the formation of mycelium with- 

 out fructification as a normal and complete development. 

 The conditions of life described above hold good not 

 only for the growth of the mycelium, but also for fructi- 

 fication and the formation of spores; it has already been 

 pointed out how necessary the presence of ox3*gen is for 

 the latter process, and in this place we need only mention 

 the few facts that are known with special reference to 

 Conditions of the act of the germination of spores. For this process 

 turn 6 forma " we do not as a rule absolutely require the presence of 

 any particular nutrient material, with the exception of a 

 large quantity of water. The formation of the germi- 

 nating tube takes place at the expense of the nutrient 

 materials which have been stored up in the spore, and it 



