ALCOHOLIC FERMENTATION— LICHENS 257 



nated Barley) is treated with hot water, and supplies part of the 

 sugar, various other sugars being used according to local practice. 

 Hops are added to the liquid to provide the peculiar flavour, 

 and the whole of this wort is then fermented in vats.' The 

 success of brewing depends upon the employment of pure races 

 of Yeast and the realisation of the right temperatures at the 

 different stages of the process ; a small supply of oxygen has 

 also been shown to be favourable to active fermentation. 



In the fermentation of sugars a considerable quantity of 

 energy is liberated, and herein possibly lies the advantage to 

 the Yeast-plant. It appears likely that some of this energy 

 is utilised in synthesis. The process of alcoholic fermentation 

 shows much resemblance to anaerobic respiration, but there is 

 this difference, that the compounds broken down are outside 

 and not within the organism, so that no loss of weight is in- 

 volved. It may be added that Yeasts are not alone among 

 Fungi in fermenting sugars, since spores of Mucor, for example, 

 if placed in a sugary liquid, will reproduce by budding and cause 

 alcoholic fermentation, forming so-called Mucor-ytd&i. 



We have already noted that a parasitic Fungus may some- 

 times do very little harm to the host, and such cases are but a 

 step removed from those in which the balance, between the 

 Fungus and the organism with which it is associated, is so perfect 

 that both are mutually benefited. Such a condition is found in 

 the Lichens, whose body is composed of algal cells embedded 

 in a weft of fungal hyphse. Lichens, with but few exceptions, 

 are subaerial, being commonly found on peaty soils, rocks, tree- 

 trunks, old walls, etc. In conjunction with various Alg£€ (com- 

 monly Cyanophyccce) and Mosses, Lichens play an exceedingly 

 important part in the primary colonisation of rock surfaces and 

 of other ground laid bare of vegetation, being conspicuous, for 

 instance, among the early vegetation of burnt heaths. The black- 

 coloured blotches, which are such a familiar sight on the pebbles 



' If all the starch in the malt is allowed to undergo conversion into 

 sugar, and the fermented product is distilled, whisky results ; brandy is 

 similarly obtained by distilling the alcohol from fermented grape- juice. 

 The Japanese saki is obtained by the fermentation of rice. 



17 



