Under synthetic tissue are grouped all tissues and cells which form substances or compounds other than protoplasm. Such compounds are stored either in special cavities or in the cells of the plant, as the glandular hairs; internal secreting cavities of barks, stems, leaves, fruits, seeds, and flowers; photosynthetic cells or cells with chlorophyll, and the parenchymatic cells which form starch, sugar, fats, alkaloids, etc. PHOTOSYNTHETIC TISSUE The most important non-glandular synthetic tissue is the photosynthetic tissue, which is composed of the chlorophyll-bearing cells of the plant. These are the so-called green cells of leaves, of stems of herbs, of young woody stems, and in the older woody stems of plants like wild cherry, birch, etc. The greater part of the tissue of leaves is composed of chlorophyll-bearing cells. Leaves collectively constitute the greatest synthetic manufacturing plant in the world, because the green cells of the leaf produce most of the food of men and animals. The two compounds utilized in the manufacture of food are carbon dioxide (CO₂) and water (H₂O). These two compounds are combined by chlorophyll through the agency of light into starch. Chemically this reaction may be expressed as follows: 6CO₂ + 5H₂O = 2C₆H₁₀O₅ + 6O₂. During the day a large quantity of starch is formed. At night through the action of a ferment the excess of starch remaining in the leaf is converted into sugar (C₆H₁₂O₆) - C₆H₁₀O₅ + H₂O = C₆H₁₂O₆. In this form it is distributed to the living cells of the plant. The presence or absence of starch in leaves is easily ascertained by placing the leaf in hot alcohol to remove the chlorophyll, and by adding Lugol’s solution. If starch is present, the contents of the cells will become bluish black; but if no starch is present, the cells remain colorless. GLANDULAR TISSUE The =glandular tissue= of the plant is divided into two groups, according to where it occurs. These groups are, first, =external= glandular tissue, and secondly, =internal= glandular tissue. The most important external glandular tissue is composed of the glandular hairs. These are divided into two groups: first, =unicellular=; and secondly, =multicellular= glandular hairs. UNICELLULAR GLANDULAR HAIRS The =unicellular glandular hairs= are either sessile or stalked. =Sessile unicellular hairs= occur in digitalis leaves. =Stalked unicellular hairs= of digitalis are shown on Plate 60, Fig. 2. =Unicellular uniseriate stalked glandular hairs= occur on the stems of the common house geranium (Plate 61, Fig. 2), on the leaves of butternut, the leaves and stems of marrubium peregrinum (Plate 98, Fig. 5), and in arnica flowers. The stalk varies from two to ten cells; in eriodictyon the cells vary from four to eight cells. Unicellular multiseriate stalked glandular hairs are not of common occurrence.