168 HOW CROPS GROW. 
a moist atmosphere. Thus arranged, suitable warmth, 
ventilation, and illumination, alone are requisite to con- 
tinue the growth until the nutriment of the seed is nearly 
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 algee 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 experienceof Nobbe & Siégert, 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 3 grams, (60 grains,) 
of chloride of potassium, with water enough to make the 
solution up to the bulk of one liter, (or quart.) Mix 80 
