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“over the trees of our forests, which have been gaunt and bare for so long during 
the dreary months of winter. For the better understanding of the special func- 
tions of the leaves, let us, fora moment, glance at the life history of a plant. 
The seed, containing the germ, is placed in the ground; under the influence of the 
warmth of the sun and a certain amount of moisture, the embryo which it 
contains begins to develop, and sends down a radicle into the soil, and a stem 
bearing the plumule, or little bud of undeveloped leaves, upwards to the light ; 
at the same time the cotyledons or seed-leaves are formed. We have, then, a 
central axis developing in two opposite directions, the lower part is called the 
descending axis or root, and the upper the ascending axis or stem. Upon this axis 
or its divisions all the future organs of the plant are arranged; those 
which immediately succeed the cotyledons are the true leaves, and 
all which succeed the leaves in the way cf development, such as 
the flower and its parts, are merely modifications of the leaves, designed 
for special purposes; therefore, the three organs which existed in the 
embryo in a rudimentary state are called the jfundimental organs of the plant, or 
organs of nutrition, because they have for their object its nutrition and develop- 
ment. Asa general rule, the plantlet exists ready formed in the seed. This can 
be easily seen by soaking a bean in water for a day or two and then opening it 
with a penknife, when there will be found a miniature stem and a pair of leaves, 
which need only be brought to the light to attain their green color. It has now 
only to form a root to fix it in the ground, when it becomes a perfect, though 
diminutive, vegetable. This root, though, can only be formed from proper material ; 
neither water nor anything else which the plant is imbibing from the earth will 
answer. ‘The proper material is prepared food, more or less of which is always 
provided by the parent plant and stored up in the seed,in the form of starch or 
similar nourishment, and generally deposited in the cotyledons or seed-leaves. 
For a short time, this small stock suffices to support the young plant, and, by 
the time that is exhausted, it has formed roots and true leaves, and is, by their 
means, able to take care of itself. 
The articles which form the diet of plants are exceedingly simple ; they 
are water, carbonic acid, and ammonia. As soonas the young plant has expanded 
its green leaves, itabsorbs these substances, from the soil by its roots and from 
the air by its leaves. It will not be difficult to understand what the organic 
constituents of plants are, and how the plant obtains them. A leaf 
consists of two parts: a woody and a cellular; the former is the frame- 
work of ribs and veins which serve to strengthen it, and also to act as canals 
to bring in the ascending sap, and to distribute it by the veinlets throughout 
every part. The cellular portion is the green pulp, and is nearly the same as the 
green layer of the bark; so that the leaf may properly enough be considered as 
an expansion of the fibrous and green layers of the bark ; the whole is covered by 
a transparent skin called the epidermis. The green pulp consists of cells of various 
forms, usually loosely arranged so as to leave many irregular spaces or air passages, 
communicating with each other throughout the whole interior of the leaf. The 
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