. Cyclopedia of farm crops. Farm produce; Agriculture. 8 STRUCTURE AND PHYSIOLOGY OF THE PLANT. Fig. 12. Leaf of apple, showing blade, petiole, and small nar- row stipules. WW Tlie stem structure. The internal structure of the plant does not give rise to such definite parts or organs as appear in the external conformation. The plant-body is made up of cells. Some of these cells perform one work and some perform another work. The fundamental tissue is parenchyma. In this tissue the cells are very simi- lar one to another, more or less cubical or equal- sided, or at least not greatly elongated.
. Cyclopedia of farm crops. Farm produce; Agriculture. 8 STRUCTURE AND PHYSIOLOGY OF THE PLANT. Fig. 12. Leaf of apple, showing blade, petiole, and small nar- row stipules. WW Tlie stem structure. The internal structure of the plant does not give rise to such definite parts or organs as appear in the external conformation. The plant-body is made up of cells. Some of these cells perform one work and some perform another work. The fundamental tissue is parenchyma. In this tissue the cells are very simi- lar one to another, more or less cubical or equal- sided, or at least not greatly elongated. The vital processes take place in the parenchyma. Out of the ' parench3'ma the other and special kinds of tissue develop. The special cellular structures in the stem are chiefly mechanical tis- sues of two general kinds of elongated cells,—those that support the plant or contribute to maintain its form and stature, those that transport the fluids. The supporting tissues, giving rigidity to the plant, are of two kinds in respect to the structure of the cell-wall: those in which the cells are thick- ened or strengthened in the angles (collenchyma, Pig. 24), and those in which the cell-walls are thickened throughout (sclerencyhma). The conducting tissues are also of two kinds : those with trachea-like walls, marked with rings or pits, and those with punctured or sieve-like walls. The supporting tissues may be in the epidermis of young or of small stems, in the bark, or placed inside the woody cylinder. The conducting tissues are usu- ally definitely placed, and these we may consider further. The development of these mechanical tis- sues (for transportation and support) results p£l- in the formation of vessels, or systems of spe- cialized tissue in particular parts of the stem. Vessel-bearing plants are said to be vascular, in distinction from certain very low orders of plants in which no special tissues of this kind have been developed. It is well known that trees of temperate
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