i;o CHEMICAL COMPOSITION OF PLANTS 



that is needed by green plants, the necessary carbon being obtained from the 

 carbon dioxide of the air : — 



Grams. 



For demonstration purposes buckwheat, barley, maize, small dwarf-beans, 

 and wallflowers are easily grown. Seeds should be germinated in damp 

 sawdust or on damp blotting-paper, and when 

 the seedlings are large enough to handle they 

 should be arranged as in Fig. 82, so that their 

 roots dip into the culture solution, their stems 

 being allowed to develop through the hole in 

 the cork {c). Seedlings of maize, barley and 

 beans may be fastened in position by means of a 

 pin pushed through the side of the pericarp or 

 the seed-coat into the lower side of the cork ; or 

 they may be supported by inserting cotton wool 

 in the hole through which the stem emerges. 



It is important to see that only the roots dip 

 into the solution : wetting the endosperm, 

 cotyledons, or hypocotyl frequently leads to ill- 

 health and death of the plant. 



The sides of the glass cylinder should be 

 covered with cardboard or several thicknesses of 

 paper to prevent access of light and heat to the 

 solution : or the cylinder may be sunk in a box 

 containing cocoa-nut fibre. 



Avoid placing the culture in the direct sun- 

 light so that the solution in which the roots are 

 immersed may remain cool. 



In experiments extending over a period of several 



Fig. 82. — Water-culture of 

 barley plant, v Cylindrical 

 glass vessel ; J culture solution : 

 c perforated cork bung. 



weeks the culture 



solution should be changed every week, and the plant should be placed 

 occasionally for a day or two with its roots in distilled water, or water con- 

 taining a small amount of calcium sulphate. 



Ex. 97. — Fit up a water-culture as above but do not add ferric chloride or 

 any other compound of iron to the solution : compare the growth of the plant 

 with one growing in a complete solution. 



Ex. 98. — Note the differences between plants growing in a complete solu- 

 tion as above and some growing in the following solutions in which nitrogen 

 and potassium are respectively missing. 



