ce Cultivation of Plants. 
baceous tissue. The cells themselves are composed of carbon, 
oxygen, and hydrogen, and their contents of the same elements, 
with the addition of nitrogen. With these essential elements 
several others are associated in different plants. The com- 
moner ones are phosphorus, sulphur, silex, potash, soda, and 
lime. The chemical compounds of organic origin are ternary, 
quaternary, or even more complicated ; whereas inorganic com- 
pounds generally are binary. Sugar and starch may be men- 
tioned as the must familiar vegetable compounds. Amongst 
vegetable acids, citric, malic, and oxalic are the commonest. 
(Juinine, cinchonine, and morphine are valuable alkaloid drugs. 
The principal phenomena of plant-life coming under our con- 
sideration are: germination, absorption, and respiration. 
1. Germination.—This is the first phase in the develop- 
ment of independent life in a plant from a seed. In order to 
accomplish this stage certain conditions are indispensable. 
These essential conditions are: warmth, moisture, andair. 'he 
temperature at which seeds will germinate varies considerably 
in different species, ranging mainly from 40° to 75° Fahrenheit. 
But the seeds of some hardy plants will vegetate at a lower 
temperature, whilst a few tropical things require a still higher 
degree of warmth to start them into life. There must be 
sufficient moisture within reach of the seed to enable it to 
burst its coat by absorption and feed the young embryo. And 
the access of air is indispensable to effect the chemical changes 
to which the contents of the seed are subject in germination for 
the use of the young plant. Unless these three conditions are 
united in their proper degrees, the seeds will soon perish, 
expecially if there be an excess of humidity. Inthe absence of 
moisture, and when not exposed to deleterious atmospheric 
or other influences, some seeds will retain their germinating 
powers for many years, whilst others will not grow after the 
first season. Most seeds contain the nourishment required 
for the support of the young plant in its earliest stage. This 
is stored up either in the embryo itself, and chiefly in the 
cotyledons, or it is present in the form of starch and other 
ingredients, in the albumen, surrounding the embryo, and 
constituting in many cases the bulk of the seed. When a seed 
ix committed to the soil, it more or less rapidly absorbs suffi- 
cient water to soften its coats and distend the tissue of the 
embryo, causing it to push forth its radicle or rootlet, which 
invariably turns downwards, no matter what the position of the 
