APPARATUS. 



249 



learning the office of each constituent. This is more satisfac- 

 torily accomplished by water-culture, which, reduced to its sim- 

 plest terms, consists in furnishing to the plant under proper 

 conditions different mineral matters in aqueous solution, and 

 noting their effects upon it. It has been long known that plants 

 can be grown to a considerable size in ordinary river-water, or 

 water holding in solution certain mineral salts. 1 But it was not 

 until 1858 that the method of water-culture w r as systematically 

 applied by Sachs, Knop, and Xobbe to the investigation of the 

 relative value and the office of the different mineral constituents 

 in the nutrition of plants. It has since been widely employed in 

 the examination both of flowering and flowerless plants. 



669. The method adopted for ordinary flowering plants is es- 

 sentially as follows : seeds are made to germinate upon some clean 

 support, for instance moist sponge or 

 cotton, horse-hair cloth, or perforated 

 parchment-paper, and when the root 

 of the seedling is a few centimeters 

 long and the plumule is somewhat 

 developed, the plantlet is secured to 

 a firm support at the surface of a cy- 

 lindrical glass vessel, in such a man- 

 ner as to allow the roots to dip into 

 the nutrient liquid which it contains, 

 while the body of the seed is not im- 

 mersed. One of the simplest sup- 

 ports for the plantlet is shown in 

 Fig. 145. A perforated cork is cut 

 in halves, and the two parts are held 

 together Ijy a spring. The pressure 

 exerted by the spring is sufficient to 

 keep the plantlet in place, and not 

 enough to injure it in any way. When the plant has attained 

 the height of a few inches, it is well to provide a firm rod at the 

 side of the cork, so that the stem can be held in place. Certain 

 precautions have been found advantageous : (1) the roots in the 

 liquid should be kept darkened ; (2) the solution should be fre- 

 quently renewed. 



When skilfully managed, this method of culture gives very 



145 



1 Woodward (Philosophical Transactions, 1699) and Duhamel (Traite des 

 Arbres, 1765) have given accounts of their cultivation of various plants in 

 this way. 



