168 HOW CROPS GROW. 



a moist atmosphere. Thus arranged, suitable warmth^ 

 ventilation, and illumination, alone are requisite to con 

 tinue the growth until tho nutriment of the seed is n early 

 exhausted. As regards illumination, this should be as full 

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

 tected from it, by enclosing the vessel in a shield of black 

 paper, as, otherwise, minute parasitic algaB would in time 

 develop upon the roots, and disturb their functions. For 

 the first days of growth, pure distilled water may advan 

 tageously surround the roots, but when the first green leaf 

 appears, they should be placed in the solution whose nu 

 tritive 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 recent experience of Nobbe & Siegert, Wolff, 

 and others, supplies valuable information on this point. 

 Prof. Wolff has obtained striking results with a variety of 

 plants in using a solution made essentially as follows : 



Place 20 grams, (300 grains,) of the fine powder of well- 

 burned bones with a half pint of water in a large glass 

 flask, heat to boiling, and add nitric acid cautiously in 

 quantity just sufficient to dissolve the bone-ash. In order 

 to remove any injurious excess of nitric acid, pour into the 

 hot liquid, solution of carbonate of potash until a slight 

 permanent turbidity is produced; then add 11 grams, (180 

 grains,) of nitrate of potash, 7 grams, (107 grains,) of 

 crystallized sulphate of magnesia, and :) grains, (60 grains,) 

 oi chloride of potassium, with water enough to make the 

 solution up to the bulk of one liter, (or quart.) Mix 30 



