32 SCIENCE AND SOIL 



It may be noted that cane sugar differs from milk sugar by one 

 molecule of water (HgO) . The sugars are a very important group 

 of compounds, but perhaps the starches are a still more important 

 group. Starch (C 6 H 10 O 6 ) appears to differ from glucose (C 6 H 12 O 6 ) by 

 one molecule of water (H 2 O) , but it is known that the starch mole- 

 cule is not simply C 6 H 10 O 5 , but some multiple of this formula, which 

 is best written (C 6 H 10 O 6 )^, in which x stands for the number by 

 which this formula should be multiplied, for as yet x is unknown, 

 although the proportion or percentage of each element in starch 

 is known. 



The formula for cellulose (plant fiber) must also be recorded as 

 (CgHjoOg)^., but this x may be a different number than the x of 

 the starch molecule. 



Growth. Rapidity of growth is related to leaf surface. Sugar, 

 starch, and fiber constitute the great carbohydrate group of plant 

 structure, and their formation is dependent primarily upon the 

 fixation of carbon, with oxygen and hydrogen, in the leaf; . and, 

 with all necessary things provided in proportionate amounts, this 

 process goes on in direct proportion to leaf surface. In other words, 

 under perfect conditions, a leaf four inches long will grow four times 

 as much during the day as a leaf only one inch long; and, with 

 sufficient moisture and with plant food provided in abundance, 

 a pasture with the grass kept six inches long will furnish twice 

 as much feed as one with the grass kept down to three inches. 



If the foundation principles and the controlling factors in plant 

 growth can be known, then the ideal conditions for crop production 

 may be provided much more nearly than is common. The ideal 

 condition is to provide all controllable factors in such abundance 

 or perfection that the crop yields will be limited only by the sun- 

 shine and rainfall. With all other limiting factors removed, the 

 average yield of corn in the corn belt would undoubtedly exceed 

 ico bushels per. acre. (See the records of actual yields, in the follow- 

 ing pages.) 



Carbon cycle. The carbon cycle includes both the fixation and 

 the liberation of carbon. Animals feed upon plants and plant prod- 

 ucts rich in carbon compounds, which in part are digested and car- 

 ried into the blood to meet the oxygen inhaled through the lungs. 

 The carbon is burned, or oxidized, to carbon dioxid, furnishing 



