182 HOW CROPS GROW. 



is nearly exhausted. As regards illumination, this should 

 be as full as possible, for the foliage ; but the roots should 

 be protected from it, by enclosing the vessel in a shield of 

 black paper, as, otherwise, minute parasitic algae would 

 in time develop upon the roots, and disturb their functions. 

 For the first days of growth, pure distilled water may ad- 

 vantageously surround the roots, but, when the first green 

 leaf appears, they should be placed in the solution whose 

 nutritive power is to be tested. The temperature should 

 be properly proportioned to the light, in imitation of what 

 is observed in the skillful management of conservatory or 

 house-plants. 



The experimenter should first learn how to produce 

 large and well-developed plants by aid of an appropriate 

 liquid, before attempting the investigation of other prob- 

 lems. For this purpose, a solution or mixture must be 

 prepared, containing in proper proportions all that the 

 plant requires, save what it can derive from the atmos- 

 phere. The experience of Nobbe and Siegert, Knop, 

 Wolff, and others,* supplies valuable information on this 

 point. Wolff has obtained striking results with a variety 

 of plants in using a solution made essentially as follows: 



Place 20 grams of the fine powder of well-burned bones 

 with a half pint of water in a large glass flask, heat to boil- 

 ing, and add nitric acid cautiously in quantity just suffi- 

 cient to dissolve the bone-ash. In order to remove any 

 injurious excess of nitric acid, pour into the boiling liq- 

 uid a solution of pure potassium carbonate until a slight 

 permanent turbidity is produced; then add 11 grams of 

 potassium nitrate, 7 grams of crystallized magnesium sul- 

 phate, and 3 grams of potassium chloride, with water 

 enough to make the solution up to the bulk of one liter. 



Wolff's solution, thus prepared, contains in 1000 parts 

 as follows, exclusive of iron: 



r.filr Landtvlrthschaft,\8&2, p. 

 637) for full and concise instructions. 



