4 FEEDS AND FEEDING 



dium, silicon, chlorin, and manganese, tho commonly present, are re- 

 garded by some authorities as not essential to plant life. 



8. Plant building. Living matter is distinguished from non-living 

 matter by its power to grow, to repair its own waste, and to reproduce 

 itself. In plants the life principle is most in evidence in the transparent, 

 viscous protoplasm found within the plant cells. Because of inherent 

 differences in the protoplasm, each plant possesses an individuality and 

 is able to grow and reproduce itself after its own manner. 



It has already been mentioned that carbon dioxid is absorbed by the 

 leaf cells from the air entering the pores on the under surface of the 

 leaves. Water and likewise nitrates and other mineral compounds taken 

 by the roots from the soil are brought to the leaves in the sap currents. 

 Here, in some mysterious manner the first plant compounds are built by 

 the protoplasm of the leaf cells thru the action of sunlight on the green- 

 colored chlorophyll of the leaf. In this process the carbon dioxid and 

 water are broken down, and the carbon, hydrogen, and some of the oxygen 

 of which these compounds are composed are rearranged or built into 

 relatively simple plant compounds. The rest of the oxygen is given 

 back to the air as free oxygen gas. It is not definitely known whether 

 the first product so formed is starch, sugar, or some simpler compound. 



From the compounds first made the plant builds more complex sub- 

 stances, some of which contain mineral matter obtained from the soil. 

 Both sugar and starch contain much energy, which may be set free as 

 heat when these substances are burned or otherwise broken up. Carbon 

 dioxid and water, on the other hand, have little, internal energy, and so 

 on being decomposed, do not liberate heat. To make sugar and starch 

 from these two energy -poor substances, the plant must receive energy 

 from some outside source.. This energy, used in building carbon dioxid 

 and water into energy-holding sugar and starch, comes from the sunlight 

 which is absorbed by the leaves. 



9. The carbohydrates. Sugar and starch, together with the related 

 products, the celluloses and pentosans, are. called carbohydrates. This 

 group of plant compounds makes up the major portion of all plant sub- 

 stance. The term carbohydrates means that these compounds are formed 

 of the three elements, carbon, hydrogen, and oxygen, the latter two being 

 present in the proportion existing in water, the chemical formula for 

 which is H 2 O. (This means that every molecule of water contains two 

 atoms of hydrogen and one atom of oxygen. ) The molecular composition 

 of the leading plant carbohydrates is as follows : 



Glucose \ PTT o Starch ) rr TT n w 



Fruit sugar/ CeHl2 6 Cellulose / ( C e H -0 5 )x 



Cane sugar ) c H O Pentose C 5 H 10 5 



Malt sugar J Pentosan (C 5 H 8 4 )x 



The molecules in the bracketed groups are in reality far more complex 

 than the formulae indicate, the actual molecule being many multiples of 

 the groups here given. 



