12 
SOILS AND ALKALI. 
the plant, and rendering it harmless. Phosphorus has 
been thought to assist in the transfer of soluble albumin¬ 
oids. Iron is necessary to develop the chlorophyll gran¬ 
ules and give the plant its green color. The nitrogen in 
combination is always present in active cells. Protoplas¬ 
mic matters in plants contain about 15 per cent, of nitro¬ 
gen in combination. At different stages in the life of a 
cell, its protoplasmic matters may pass through consider¬ 
able changes of form and structure, as indicated in an ex¬ 
amination of a ripening seed ; but under all these varying 
conditions, nitrogen in combination is never absent from 
the living substance of the plant. For the formation of 
new protoplasmic matters in the plant, supplies of nitrogen 
in an available form must be furnished; for healthful 
growth, these supplies must be adequate in amount, hence 
the importance of a fertilizer containing nitrogen, either 
as ammonia or nitric acid. Having seen that the soil, the 
principal medium in which roots extend, possesses the 
power of absorbing and retaining water, saline matters 
and gases, we must direct our attention to the conditions 
upon which the root hairs (fibrous roots) can abstract from 
it the matters requisite for the plant. These conditions are 
(1) presence of free oxygen, (2) certain temperature, (3) the 
presence of saline matters in an available form in the soil. 
The fertility of the soil depends upon many conditions, 
as temperature, rainfall, elevation above the sea level, etc., 
as well as its chemical composition. The experiments of 
Messrs. Laws and Gilbert have shown that most soils have 
a natural fertility and can raise the same crop for a num¬ 
ber of years with but little diminution in the crop. 
There are two kinds of soil analysis: Mechanical and 
chemical. Great stress was formerly laid upon the 
mechanical analysis of soil. The principle is quite simple. 
Water is commonly made use of to separate the soil into 
coarse and fine particles, or the same thing can be accom¬ 
plished by metal sieves ranging from 10 to 100 meshes to 
the square inch, a weighed quantity of the soil being 
taken, and the portion remaining on each sieve being col¬ 
lected and weighed. The chemical analysis is quite long 
and tedious, and the selection of the soil is one of the most 
important operations to be performed. It is almost impos- 
