AGRICULTURAL CHEMISTRY. 149 



potassium starvation. Potash apparentlj" aids in the transportation of 

 the starch grains through the cell walls. Its movements within the plant 

 are in the same direction as the starch. When any plant is unable to ob- 

 tain its normal amount of potassium, its growth is checked and the plant, 

 in the course of a short time, passes into a decline. 



When the different elements that are found in the ashes of plants were 

 flrst determined, it was supposed that a chemical analysis of the ash 

 would show just what kind of mineral food different plants would require. 

 This idea gave rise to all kinds of speculations, and chemists labored away 

 making chemical analyses of the ashes of plants with the hope of finding 

 just how much and what kinds of minerals should be used for the best 

 results. Finally, these various speculations were put to trial, and then 

 in many cases it was found that the plants grew no better than they did 

 before, showing that there was yet another undetermined factor. 



It was shown by Liebig that when a manure pile was divided into two 

 equal parts, and one part burned to ashes and the ashes applied, while, on 

 the other hand, the manure was applied directly to the crop, that the ma- 

 nure when applied directly was far more effectual than when only the ashes 

 were used. Why this difference when there was the same quantity of each 

 available ash element in both cases, and all of the minerals necessary for 

 plant development were the same in each, and yet the practical results 

 were not the same? 



The reason for this difference was soon explained when nitrogen was 

 shown to be a. necessary element for plant growth. When the manure 

 was burned the nitrogen was liberated and escaped into the air in the 

 form of gaseous combinations, and when the manure was applied directly 

 the nitrogen was available as plant food. There has been more experi- 

 menting done with the nitrogen supply of plants than in any other line 

 of similar work, and as the result of all of this labor many valuable results 

 have been obtained. Only a limited number of plants are capable of tak- 

 ing their nitrogen supply directly from the air, while the larger number 

 must be supplied with this element from the soil. The nitrogen supplied 

 for plants and crops is the most important factor, economically consid- 

 ered, of all of the elements that are necessary for plant food. The com- 

 mercial value of nitrogen is a little more than double that of phosphoric 

 acid, and about four times that of potash. 



The necessity for concentrated fertilizers has not as yet made itself 

 felt, and it is to be hoped will not for some time to come, and as long 

 as the local demand for such materials as tankage and dried blood is 

 no greater than it is at present, they will continue to supply us with all 

 the concentrated nitrogen that we may desire for any special purposes. 



The draft of horticultural products upon the soil is not great,in fact, it 

 is less than any other branch of husbandry. A hundred pounds of red 

 raspberries take less than one-half a pound of mineral matters from the 

 soil, potatoes less than a pound. The mineral matter that is lost in the 

 weed crop of many gardens is frequently ten times greater than that 

 removed in any ordinary horticultural crop. 



The beneficial results of systematic horticulture, especially forestry, 

 are many. A tree always improves a soil by enriching it with the humus 

 formed from the decaying leaves, and the humus then renders more 

 plant food available than the tree has itself taken up; hence, trees cause 

 soil to grow richer and richer. 



