240 ECONOMIC MYCOLOGY. 



tlie sugar of commerce, or cane sugar, is made up, like starch, of carbou 

 and water ; but the proportions differ. Instead of six to five, in saccha- 

 rose it is twelve to eleven. This siagar is found in the maple and beet ; 

 whenever found it is intended as a store for the future use of the plant 

 at the time when a great and sudden demand is made for the purposes 

 of reproduction. Glucose is the sugar met with in the grape and other 

 fruits ; it contains a httle more water than saccharose and is more 

 soluble. It is necessary that stored-up starch and saccharose should be 

 altered into glucose before they are used by the jilant. This alteration is 

 always prepared for by the lajdng up of nitrogenous matter in close 

 approximation with the stored material. When the food is wanted, the 

 nitrogenous matter acts as indirect feiinent, and causes the starch or 

 saccharose, whichever it may be, to take up an additional quantity of 

 water and become glucose. Thus the starch stored up in the barleycorn 

 is altered into glucose when heat and moisture bring the nitrogenous 

 matter called diastase (which has been laid up under the cuticle) in contact 

 with it. This process takes place in seeds when they germinate, and is 

 taken advantage of by the maltster. For the same reason the tuber of the 

 potato becomes sweet and transparent from the alteration of its sugar 

 into glucose when growth begins. Again, when sugar cane and beet 

 blossom a large supx^ly of nutriment is suddenly wanted ; the stored-up 

 saccharose is then digested ; that is, altered into glucose, and is carried 

 away in the sap to the reproductive organs, to be there reconverted into 

 starch, and stored up again in the seed. Parsnips and some other sweet 

 roots that do not blossom the first year, lay up glucose itself, which is 

 held in resei-ve till the next summer, then seed is formed and the root 

 loses its sweetness and collapses. 



If yeast be placed in water containing air or oxygen, the oxygen 

 gradually disappears and is replaced by carbonic acid ; a process 

 exactly similar to the respiration of fishes, continuing day and niglit, but 

 proportionately more active. The yeast would die when the oxygen was 

 absorbed, but if glucose be then added, the fungus will abstract from it 

 the oxygen required, and sot free carbonic acid and alcohol. Pasteur, 

 who has given great attention to tlie life-history of ferments, has 

 concluded, after many experiments, that a continued supply of oxygen 

 and the combustion it causes are necessary sources of energy for the 

 development of vitality in ferment plants. As soon as the cells of yeast 

 have exhausted the glucose in contact with them they have a tendency 

 to come to the surface and take on their aerial gi'owth, which is simply 

 the formation of spores. Under favourable circumstances some of the 

 cells at the surface may be observed under the microscope to form an 

 additional internal membrane, which, becoming septose, divides the proto- 

 plasm into three or four parts ; each of these parts becomes spherical, 

 opaque, and is ultimately detached as a spore. The nutrition of yeast in 

 one particular resembles that of the higher orders of plants, for it is 

 supplied with a soluble nitrogenous ferment which enables it to alter 

 saccharose. This nitrogenous matter may be separated by washing the 

 cells in water, every time they are washed some of it is dissolved out, it 

 is always acid, and if neutralised becomes again acid, directly that it 



