THE ESSENTIAL ELEMENTS 



419 



culture method was resuscitated by Sachs, who succeeded in growing healthy 

 plants by alternately transferring them from one solution, containing a portion of 

 the ash constituents, to another which contained the remainder, while Knop grew 

 plants successfully in a 

 single solution containing 

 all the essential mineral 

 constituents. Numerous 

 researches have been per- 

 formed in the latter manner, 

 and it has been found pos- 

 sible to obtain perfectly 

 normal growth and de- 

 velopment in various higher 

 plants, when grown in 

 watery culture - solutions, 

 although it does not follow 

 that all plants which grow in 

 a soil rich in humus can be 

 cultivated in this manner, 

 for the root-system is under 

 much more favourable con- 

 ditions in such a soil than 

 it is in a watery culture- 

 solution l (Sec. 28). 



In Fig. 6 1 the effects 

 of the absence of iron and 

 potassium are shown (cf. 

 also Fig. 60, p. 397). The 

 glass vessel g contains the 

 nutrient fluid, and the plant 

 is fixed in the median aper- 

 ture of the porcelain lid 

 by means of a halved cork 

 previously soaked in para- 

 fin. Young seedlings are 

 preferably employed and 

 the seeds may be germi- 

 nated in sawdust, or be- 

 tween moist filter-paper, or when all absorption of mineral constituents is to be avoided 

 from the commencement, they may be allowed to germinate on gauze netting 



FlG. 61. Water-cultures of Buckwheat. (A) without potassium, (B) in 

 normal nutrient solution, (C) without iron. 



1 Woodward, Phil. Trans., 1699, Vol. XXI, p. 208; Duhamel, Naturgesch. d. Baume, 1765, 

 Bd. II, p. 160; Sachs, Sitzungsb. d. Wien. Akad., 1858, Bd. xxvi, p. 331 ; Versuchsst., 1860, Bd. 11, 

 pp. 22, 224; Knop, ibid., 1861, Bd. Ill, p. 295; Stohmann, Ann. d. Chem. u. Pharm., 1862, 

 Bd. cxxi, p. 314; and numerous works by Nobbe, Wolff, &c., mentioned in Jahresb. f. Agr.- 

 Chem. for 1861 and following years. 



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