THE PLANT 87 



(2) I'he Sugars. — Of these there are many varieties for an 

 account of which a text-book on organic chemistry should be 

 consulted. Only a brief mention of the following can be 

 made here : 



Cane sugar, saccharose, ^\%^2p\v occurs in many plants, 

 generally in the sap ; it is especially abundant in the juice of 

 the sugar cane (16 or 18 per cent.) in the sugar beet (10 to 18 

 per cent.), and in the sap of the sugar maple. It melts at 

 1G0°C. and becomes brown at about 190° 0. It does not 

 reduce copper salts, but rotates the plane of polarised light to 

 the right. By the action of certain enzymes, e.g., invertase, 

 present in yeast, or by boiling with dilute acids, it is converted 

 into a mixture of levulose and dextrose (^^ inversion "). 



Milk sugar, lactose, Cj^II^jO,, + lip. see p. 185. 



Dextrose, glucose, grape sugar, CgHj^Og, occurs in many fruits 

 and can be obtained by boiling starch or cellulose with dilute 

 sulphuric acid. It reduces copper salts in alkaline solution and 

 rotates polarised light to the right. 



Levulose, fructose or fruit sugar, has the same empiric com- 

 position as dextrose, but rotates the plane of polarised light 

 strongly to the left. It occurs in many fruits, and, like 

 glucose, lactose and maltose (Cj.,HgjOii + II^O, formed by the 

 action of diastase upon starch), reduces copper salts to red 

 cuprous oxide in alkaline solution. 



Milk sugar, dextrose and levulose are much less sweet to the 

 taste than cane sugar. 



II. Fats and Waxes.— Fats are substances whose constitu- 

 tion has been fairly completely investigated. They, like the 

 carbohydrates, contain only the elements carbon, hydrogen, 

 and oxygen, but the latter element is present in comparatively 

 small quantities, and consequently fats are capable of uniting 

 with considerably more oxygen, thus producing much heat or 

 energy by their oxidation. 



All true fats may be regarded as compounds of organic acids 

 with an organic basic radical, glyceryl (CjHj). This radical is 

 trivalent, having the constitution: 



