ABSOEPTION OF FOOD MATEKIALS 127 



duced by the addition of certain compounds to the culture 

 fluid, or how the absence of any particular salt affects their 

 well-being. 



In carrying out experiments in this way, it is usual to sow 

 some large seeds, such as those of the broad bean, in damp 

 sawdust, and allow them to germinate. When the radicle 

 of the seedling has elongated to the extent of about an 

 inch, the seed is placed upon a perforated cork inserted into 

 the neck of a bottle containing the liquid which is the 

 subject of the investigation. It is so arranged that the 

 radicle dips down through the cork into the liquid. As 

 growth proceeds the radicle develops a root-system in the 

 way appropriate to the particular plant used, which absorbs 

 from the liquid the salts which are required by it, so far as 

 these are present. At the same time the plumule grows 

 upwards, and soon a shoot appears, which develops pari 

 passu with the root. 



By this method various plants can be cultivated with 

 different degrees of success ; in some cases not only leaves, 

 but flowers and even fruit can be produced. The progress 

 of the plant, and the readiness with which it will develop, 

 will depend upon the salts which are supplied to it in the 

 water, if it is maintained in normal conditions of light, 

 temperature, and aeration. In preparing the solution, 

 particular mixtures can be employed, and the most favour- 

 able one ascertained, while subsequent analysis of the 

 liquid will show to what extent the various constituents of 

 the culture fluid have been abstracted from it. 



This method is, however, only of use in determining 

 particular points, such as the effect of the presence of 

 certain metals in particular combinations, or the influence 

 of different concentrations of particular substances. It 

 does not give an account of what is happening to a 

 plant with its roots embedded in the soil, for the com- 

 position of the latter cannot be compared with that of 

 a solution definitely made up for purposes of experiment. 

 The composition of the soil, as we have seen, is very far 



