No. 6. DEPARTMENT OF AGRICULTURE. 667 



each bears to the productive activity of the plant. Possibly the de- 

 velopment oi" sugiir iu the beet may be cited as that example which 

 shows the highest measure of attainment of intelligent control on 

 the part of the producer over the productive action of the plaot. 

 The relations of the air and soil, as sources of the raw materials 

 from which plants are built up, have also been very carefully worked 

 out. The means by which the carbonic acid of the air, and the 

 water are brought into the plant and the transformations they un- 

 dergo in the production of the pdncipal portion by weight, of the 

 plant and materials, have been, to a quite advaoced degree, de- 

 ciphered. 



Concerning the mineral elements, our investigations have thus 



far been less productive of decisive results. Thousands of ash 

 analyses have made clear what elements the plants take up and 

 numerous painstaking water cultures have enabled us to select 

 from these ash constituefits those which are essential to the develop- 

 ment of plants; but as yet, we know very little about the specific 

 usefulness of any one of these ash constituents. Many attempts 

 have been made to discover the powers of the several common species 

 of farm plants to secure the necessary ash constituents from the sev- 

 eral mineral materials of the soil. Some little insight has been 

 gained, but the study has proven much more complex than at first 

 anticipated and our present information upon this point is quite 

 chaotic. We have, however, gained a much better conception of the 

 means by which plants are able to take up mineral materials of the 

 soil than was possessed in the year 1800. At that time, it was com- 

 monly supposed that plants actually had the power of taking in the 

 fine solid particles in the solid form and utilizing them, while others 

 held that only the humus of the soil was capable of acting as plant 

 food. To-daj, we know that most soluble substances in the soil 

 can be taken up by the plant by the same kind of process by which 

 cane sugar, spread over a dish of berries, passes through their outer 

 skins and sweetens them. We know also that very many mineral 

 substances, insoluble in water, can be taken into the plant rootlets, 

 just as the sugar is taken into the berry, and it is also quite well es- 

 tablished that an important part of the humus is likewise capable of 

 being taken up by the plant roots. Half-way through the past cen- 

 tury, it was confidently predicted that the chemical analysis of soils 

 would soon enable us to determine, in connection with the facts estab- 

 lished by the analysis of plants, precisely what kind and how much 

 fertilizer would need to be applied to a given soil to produce, under 

 fair conditions of weather, a crop of given quantity. But after fifty 

 years of patient, painstaking investigations we seem to be little 

 nearer that point than we were at their inception. This may seem 

 strange, but if I say to you that the problem that the chemist con- 

 fronts in this case is that of securing a solvent which will, in the 



