No. 6. DEPARTMENT OF AGRICULTURE. 327 



lluid. Fruit juices and infusions undergo an apparently spontaneous 

 fermentation, the sugar being converted into alcohol through the 

 agency of the yeast plant, with the subsequent conversion of the 

 alcohol into acetic acid. 



Many bacteria are, howevur, capable of directly converting sugar 

 into one or more of the organic acid«, without the intervention of 

 alcohol; in fact, it may be said that the ability to convert sugar into 

 one or more of the organic acids is almost a universal property of 

 bacteria, although they vary among themselves as regards kinds and 

 quantities of acids produced. 



In order to better understand the fermentation of the different 

 carbohydrate constituents of plants, it will be best to consider them 

 in turn. 



(a) T/ie Conversion of Starch into Sugar. When seeds germinate, 

 a marked change takes place, the most notable of which is an altera- 

 tion and an eventual solution of the starch granules which fill the 

 cells. In proportion as the starch disappears there is a correspond- 

 ing increase in sugar. In the prejiaration of malt from barley the same 

 change takes place. The barley grains are allowed to sprout under 

 favorable conditions of heat and moisture, during which a consider- 

 able proportion of the insoluble starch, is converted into a soluble 

 sugar. If a quantity of this malt be steeped in water, especially if 

 the malt be macerated to a pulp, the greater portion of the sugar, a 

 part of the soluble starch and dextrine bodies and other extractive 

 matter pasiS into solution. If a portion of this extract of malt be al- 

 lowed to act upon starch it will be found to possess the powder of con- 

 verting the starch into sugar. Furthermore, if several volumes of 

 strong alcohol be added to a volume of the malt extract a whitish pre- 

 cipitate will be thrown down, which can be collected on a filter and 

 redissolved in a small quantity of water. If now this watery solu- 

 tion be allowed to again act upon starch, it will be found to possess 

 properties identical with that of the simple infusion. 



Malt extract, therefore, contains a substance which is precipitated 

 by alcohol and which has the power of converting starch into sugar. 

 This substance is called diastase or amylase. 



Diastase has an important function in relation to the nutrition of 

 plants. Plant food exists largely in the form of starch, but which 

 in this shape is of no use, since it is insoluble and therefore incapable 

 of being carried in solution to growing parts; in short, the starchy 

 food of the seed must be digested before it is available, and this di- 

 gestion is effected through the agency of diastase. Similarly, starch 

 is formed in the leaves and other green organs of the plant, but be- 

 fore it can be utilized as food it must be converted into sugar. To 

 effect this change diastase is present in all leaves and organs where 



