102 



PLANT PRODUCTS 



be freed by the combustion of dry plant materials equals 

 the amount of solar energy necessary for their production, 

 and the animal energy obtained by consuming plant 

 products will also be the same amount less some forms of 

 waste (discussed in Part IV.) . Although the actual mechanism 

 by means of which carbon dioxide is converted into complex 

 organic bodies is only very little known, the substances 

 themselves have been the subject of much elaborate inquiry. 

 The following table gives, in brief form, the chief classes 

 of substances which are produced in plants by these means. 



^Water- 



Organic 

 matter "^ 



'Vegetable 

 acids 



Carbo- 

 hydrates 



Fats and 

 oils 



\ Nitrogenous 

 bodies 



\ Mineral matter 



Table 19. 



Volatile, such as acetic acid. 

 Non-volatile. Lactic, citric, tar- 

 taric, oxalic acids. 



Pentosans (gums) as araban 



and xylan. 

 Pentoses (sugars) as arabi- 



nose and xylose. 

 Furfuroids, lignin, etc. 

 Hexosans (amylans) as cel- 

 lulose and starch. 

 Hexoses (glucoses) as 



dextrose, levulose. 

 Poly - saccharoses as 

 cane sugar, etc. 

 True fats and oils. 



Wax. 



Resins and essential oils. 

 Proteins. 



Amides and Amines. 



' Phosphates of lime, potash, and 



other bases. 

 Sulphates of lime, potash, and 



other bases. 

 Silicates of lime, potash, and 

 other bases. 

 \, Chlorides of sodium, etc. 



Feeding value. 



I Practically 

 none. 



Doubtful. 



Do. 



None. 



Heat-pro- 

 ducers. 



Heat pro- 

 ducers. 



No value. 

 Do. 



Flesh- 

 formers. 



Small heat- 

 ing values. 



Bone - form- 

 ing. 



None. 



None. 



ive. 



In some cases they are very well-known organic substances, 

 in others they are substances only described in the advanced 

 text-books. 



The Vegetabi^e Acids. 



Formic Acid, H.COOH, occurs in small quantities in 

 stings of nettles, in butter exposed to sunlight, in the contents 

 of the stomach, and in many fermented materials. Formic 



