170 MICRO-ORGANISMS AND FERMENTATION. 



many fungi a large number of these spore tubes may occur 

 combined to form fruit-like clusters, as seen in Fig. 34. 



Lastly, it may be stated that there are yet other 

 forms of reproduction occurring in the moulds. We must 

 pass over their detailed description, and only mention that 

 many species possess specially constituted resistant spores 

 (to which class the zygospores belong), which enable the fungus 

 to preserve its vitality for a long period even under the most 

 unfavourable conditions. Although apparently very fragile. 

 in reality they share with bacteria the power of offering a very 

 stubborn resistance to attacks from without, and can maintain 

 their vitality for many years. 



When ripe, the spore is capable of germinating. An 

 example of the development of a Penicillium conidium is given 

 in Fig. 33. The very minute spherical cell first absorbs water, 

 and its volume soon increases to many times the original size. 

 The cell-wall then commences to bulge out at a certain point, 

 the outgrowth gradually lengthening into a thread-like process, 

 which is soon cut off from the mother cell by a transverse 

 wall. The growth of the filament continues, branches are 

 given off, and new transverse walls are formed. Where the 

 spore is furnished with a strongly thickened outer coat, as 

 in the zygospore of Mucor (Fig. 35), it is ruptured by the 

 pressure exerted by the underlying inner coat which grows 

 out to form the germinal hypha. 



The spores of fungi are more resistant than the mycelium. 

 E. C. Hansen has shown, for instance, that the spores of a 

 species of Penicillium were capable of germination after having 

 been kept dry for twenty-one years. According to the same 

 author, a crop of Aspergillus glaucus was obtained from dried 

 spores after the lapse of sixteen years. The spores of many 

 species can endure very high temperatures, especially when 

 in the dry state. Thus dry Penicillium spores withstood a 

 temperature of 120 C., but when damp they were killed at 

 100 C. The remarkable power of resistance to high tempera- 

 tures, which range far beyond that at which albumen coagu- 

 lates, has been explained by assuming that the albumen 

 present in the spores is so highly concentrated that the small 

 quantity of water present is insufficient to bring about coagu- 



