36 



be immersed in sucb solutions. By varying these solutions, from some 

 omitting one, and from others another of the ash ingredients, and 

 otherwise varying their cpmposition, and noting in which one the plants 

 attain their normal growth, it is learned which of the ingredients are 

 essential and which are not essential to the plant's normal develop- 

 ment. 



Nearly all of the most valuable researches in water-culture have been 

 made by German chemists, among whom Knop, Sachs, Nobbe, Siegert, 

 Wolff, and Kuehn have been most prominent. Plants have been raised 

 in this way as large, as health}', and as perfect as when grown in the 

 soil. Nobbe obtained a plant of Japanese buckwheat nine feet high, 

 weighing, air-dry, 4,786 fold the 'weight of the seed, and bearing 790 

 ripe and 108 imperfect seeds. (Vs.-St., X, 1809, p. 1.) And Knop 

 delights in showing his friends a young oak tree whose growth has, 

 thus far, been normal, though its roots have only been imn^ersed in 

 aqueous solution. 



As the general result of these experiments it appears that, besides 

 carbon, ox.vgen, hydrogen, and nitrogen, which, though indispensable, 

 are not reckoned among the mineral or ash ingredients, potash, lime, 

 magnesia, iron, phosphoric acid and sulphuric acid are absolutely 

 necessary for the life and normal growth of agricultural plants. Chlo- 

 rine seems also to be needful for the perfect development of some 

 plants, as buckwheat and vetches. As regards soda, it appears that but 

 a minute amount, if any, is essential, while silica seems not to be an 

 essential ingredient of the food of the more common cultivated plants, 

 though Bretschneider, (Boffmann's Yahresbericht d. Ag.Chem.,1808-'69, 

 p. 238,; as the result of a number of experiments, arrives at a contrary 

 conclusion. (See, also, Johnson's " How Crops Grow," pp. 107-201.) 



After finding what are the essential ingredients of plants, the next 

 step would evidently be to determine what is the especial office of each 

 in the vital processes of the plant. 



The observation was made by Gris, ili 1843, and has since been sub- 

 stnntiated by the works of numerous experimenters, that iron is need- 

 ful to the development of chlorophyll in the leaves of the plant. Nobbe 

 (Vs. St., IV, p. 339; VI, p. Ill ; and VII, p. 374) and Leydhecker (Vs.-St., 

 Vill, i>. 180) have shown that chlorine is necessary to the normal forma- 

 tion of seeds of the buckwheat-plant ; that without chlorine the trans- 

 fer of starch from the foliage, where it is elaborated to the flower and 

 fruit, is impeded, while the leaves and stem become peculiarly diseased. 

 Tl)ese results are corroborated by experiments of Beyer, (Vs.-St., XI, p. 

 202,) while Knop has concluded, from a series of. experiments with 

 maize, buckwheat, cress, oak, and horse-chestnut, in solutions free from 

 chlorine, that the latter element is not necessary to the perfection of the 

 plant. (Chem. Centralblatt, 1809, p. 177.) 



Of the functions of the other ash ingredients almost nothing is known. 

 To discover what is the part which each plays in the vital processes of 

 the i)lant has b^en the object of an extended course of experiments 

 at the station at Tharand, which commenced in 1809, and are still in 

 process. The chief attention has thus far been given to the discovery 

 of the function of potash, and some very interesting results have been 

 obtained. 



Two series of experiments were carried out, one with Japanese 

 buckwheat, (Vs.-St., XIII, 1871, p. 321,) and the other with summer rye, 

 (Vs.-St., XII I-p. 401.) 



Experiments on the function of potash in the luclacheat plant. — The 

 questions proposed by Xobbe for solution by these experiments were — 



