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The Stem of Plants. 



The stein of plants, as soon as nutriment is conveyed to it by the 

 roots, is rapidly forced upward. Its cylindrical form is thought to be 

 much in consequence of its seeking so earnestly to reach the surface, 

 being impelled upward by the sap and, at the same time, pressed upon 

 by the surrounding earth. Its points, or opening bud, are the plumule 

 or plume, which is fed by the matter stored in the seed leaves, and 

 furnished to it by the radicle. This matter is not exhausted before the 

 proper leaves appear to furnish the required nutriment from the air. 

 When the stem first appears it is weak and brittle ; and the first object 

 of the leaves is to supply its exterior part with a woody substance, com- 

 posed of fine tough tubes that pass downwards through the cellular 

 tissue, giving it strength and flexibility ; and also to form the bark 

 according to the wants of the plant and the abundance of the leaves 

 it is to possess. The woody matter first forms a ring within the exte- 

 rior, leaving a space in the centre for the pith, and thereby forming 

 3 parts, the pith, wood, and bark. The wood is formed perpendicularly 

 and the bark and pith horizontally ; and the last two are connected by 

 cellular tissue. The wood part when wounded is healed by the cellu- 

 lar or horizontal parts, forming granulations which coalesce. Some 

 plants suffer great lacerations, but readily close the wounds. 



The membranous parts of plants are the cellular texture and the vas- 

 cular texture. The first is composed of small cells, like honey-comb, 

 or like the cellular system in animals containing the fat of the body. 

 In vegetables the cells contain resinous, oily or saccharine juices, and 

 sometimes air only. They compose the principal part of the pith of 

 plants. This texture also abounds in fleshy and pxilpy fruits, tuberous 

 roots and stems of grasses. It is situated in the bark under the ex- 

 terior, or cuticle. Being filled with juice, it gives to plants their 

 color, which is mostly green, in the same manner as the texture be- 

 neath the cuticle of the human skin gives color to man. These juices 

 also give color to flowers and leaves. Cells are principally filled with 

 water in young plants, while old ones are often empty. 



The vascular texture is composed of tubes, like the blood vessels of 

 the human body. These are opened at botli ends and lined with a 

 cellular substance. They extend throughout the plant, transmitting 

 air, etc., to its various parts. Those which are entire, or without per- 

 forations, convey the proper juices containing oils and resinous matter, 

 and those which are porous partake of the character of the cellular 

 parts. 



The spiral and annular vessels are so called from their form, the 1st 

 resembling that of a screw, and the 2d that of a ring. The spiral 

 are formed of a fine thread, turning from right to left, and in the an- 



