YEAST. 33 



of its source is not always an easy task, being sometimes well- 

 nigh impossible. 



SILK. Scrape some threads, as in case of linen, and mount 

 in water. With both low and high powers the fibres appear 

 about the same shining, dense, cylindrical, structureless, with- 

 out central canal, easily distinguished from all other spun fibres 

 (Fig. 26, A). Silt is animal in origin and gives the same reac- 

 tions as wool. Several other bast fibres are very valuable in 

 textile industries and present appearances similar to that of 

 linen. 



Hemp is derived from Cannabis sativa, jute from Corchorus 

 olitorius and Corchorus capsularis, Manila hemp from Musa 

 textilis. More detailed study of various fibres may be found 

 in some large work, for example, Die Mikroskopie der technisch- 

 verwendeten Faserstoffe, by von Hohnel. 



CHAPTER III. 



YEAST (TORULA OR SACCHAROMYCES CEREVISLE). 



This is a plant and is that which causes alcoholic fermenta- 

 tion in sugar solutions. It is a plant of the simplest kind, con- 

 sisting of a single cell. Plants are divided into four series 

 according to their complexity of structure and functions. 



Thallophyta-(Thallus plants) j Cryptogamia or Flowerless 



Bryophyta (Moss plants) [ plants. 



Pteridophyta (Fern plants) J 



Spermaphyta or Phanerogamia or Flowering plants. 



The Thallophyta are a large group of plants in which there 

 is no clear differentiation of the plant body into root, stem and 

 leaf. A vast number of forms are included, which differ greatly 

 among themselves in complexity, but even the highest forms 

 never have true roots, and in the great majority of cases there 

 is no differentiation into stem and leaves. There is never a 

 clear differentiation into epidermal, fundamental and fibro-vas- 

 cular systems of tissues as in the ferns and flowering plants. 



The Thallophyta are divided into a number of classes, one of 

 which is called Fungi) or Moulds. It is thought by some that 

 yeast belongs to the fungi, being a degenerate form. Yeast 

 occurs both wild as well as cultivated, the former living upon 

 fruits or in fruit juices and occurring in the air, the latter be- 

 ing employed in brewing and for making bread, etc. There are 

 a number of species of wild and cultivated yeasts, and it is prob- 

 able that cultivated yeasts are descended from similar forms 

 of wild veasts. Saccharomvces cerevisise, or brewers' yeast, is 



