THE president's ADDRESS. 457 



reproduction occurs when the yeast is placed under conditions 

 where very little food is available. 



A third mode of reproduction, of a sexual nature, has quite 

 recently been observed in some of the yeasts. This method is 

 known as conjugation, and consists in the blending of the nuclei 

 of two morphologically similar cells, as met with in the Zygo- 

 mycetes, or Mucors, fungi much more highly differentiated than 

 the yeasts. Probably the latter are not so truly primitive as their 

 present structure might lead us to believe, but rather represent 

 degraded forms of higher types. 



All yeasts require oxygen for the performance of their vital 

 functions. Certain kinds obtain this gas directly from the 

 atmosphere, with which they must necessarily be in contact 

 when growing ; such yeasts are described as aerobic. Others 

 again, called anaerobic, do not obtain their oxygen from the 

 atmosphere, but by the decomposition of compounds containing 

 this element ; such yeasts can pursue their course of life in an 

 atmosphere devoid of oxygen. 



Much more is known respecting the yeasts from a scientific 

 standpoint, on account of their importance in the brewing 

 industry, than would otherwise be the case. The fact that the 

 revenue benefits to the annual amount of over o£3 2,000,000, 

 dii'ectly and indirectly connected with this industry, of which 

 over <£ 13,000,000 is derived from beer, gives some idea of the 

 enormous amount of capital at stake in this country alone, and 

 depending entirely on the utilisation of a by-product — alcohol — 

 furnished by the yeast plant. The enormous amount of carbonic 

 acid liberated during the process of brewing escapes into the 

 atmosphere, where it is used by plants. 



In the process of brewing it was the custom at one time, when 

 the wort was ready for fermenting, to leave it exposed and trust 

 to the yeasts always floating in the air settling on it and setting 

 up fermentation. This was succeeded by the practice of placing 

 a certain amount of yeast, obtained from the previous brew, into 



