How tJie Plant Grows. 



II. How the Chemist Grroups Plant Substances. 



16. Illustrations. The agricultural chemist divides plant sub- 

 stances into groups, differing in some cases from those made by 

 the physiological chemist. In the following table a few stock 

 feeds are shown as grouped by the agricultural chemist, such pres- 

 entation being for the purpose of guiding the student in his con- 

 sideration of this subject. 



Composition of certain American feeding stuffs, as arranged by the 

 agricultural chemist. 



The first column presents the names of the feeding stuffs exam- 

 ined. The second column states the number of analyses from 

 which the subsequent data are derived. As a rule these analyses 

 have been made by chemists at different points in the country, so 

 that when a considerable number have been secured we may 

 regard the average as representative of the plant or plant sub- 

 stances under consideration. The remainder of the table comes 

 under the general heading " Percentage composition." Let us 

 consider its several divisions. 



17. Water. The chemist places a small quantity of the food 

 material, usually finely divided by chopping or grinding, into a 

 small vessel and ascertains its weight. The balance used is so 

 delicate that a thimbleful of corn meal can be weighed with a 

 smaller percentage of probable error than is usual when a farmer 

 weighs a wagon-load of corn on a good scale. The sample is 

 then placed in an oven, where it is dried at a temperature of 212 

 Fahr. for several hours, or until a constant weight is secured. 

 The heat drives off the water, and the difference between the two 



