The =bast fibres= of the different rubus species (Plate 65, Fig. 7) contain starch. The medullary rays of quassia (Plate 107, Fig. 2) contain starch; while the medullary rays of canella alba contain rosette crystals. In a cross-section of canella alba (Plate 81, Fig. 3) the crystals form parallel radiating lines which, upon closer examination, are seen to be medullary rays, in each cell of which a crystal usually occurs. The =epidermal and hypodermal cells of leaves= serve as water-storage tissue. These cells usually appear empty in a section. The barks of many plants--_i.e._, quebracho, witch-hazel, cascara, frangula, the leaves of senna and coca, and the root of licorice--contain numerous crystals. These crystals occur in special storage cells--=crystal cells= (Plate 65, Fig. 6)--which usually form a completely enveloping layer around the bast fibres. These cells are usually the smallest cells of the plant in which they occur, and with but few exceptions each cell contains but a single crystal. The epidermal cells of senna leaves and the epidermal cells of mustard are filled with mucilage; the walls even consist of mucilage. Such cells are always diagnostic in powders. STORAGE WALLS =Storage walls= (Plates 68 and 69) occur in colchicum seed, saw palmetto seed, areca nut, nux vomica, and Saint Ignatius’s bean. In each of these seeds the walls are strongly and characteristically thickened and pitted. In no two plants are they alike, and in each plant they are important diagnostic characters. Storage cell walls consist of reserve cellulose, a form of cellulose which is rendered soluble by ferments, and utilized as food during the growth of the seed. Reserve cellulose is hard, bony, and of a waxy lustre when dry. Upon boiling in water the walls swell and become soft. The structure of the reserve cellulose varies greatly in the different seeds in which it occurs in the thickness of the walls and in the number and character of the pores. [Illustration: PLATE 68 RESERVE CELLULOSE 1. Saw palmetto (_Serenoa serrulata_, [Michaux] Hook., f.). 2. Areca nut (_Areca catechu_, L.). 3. Colchicum seed (_Colchicum autumnale_, L.). 3-_A_. Porous side wall. 3-_B_. Cell cavity above the side wall.] [Illustration: PLATE 69 RESERVE CELLULOSE 1. Endosperm of nux vomica (_Strychnos nux vomica_, L.). 2. Endosperm of St. Ignatia bean (_Strychnos ignatii_, Berg.).] CHAPTER IX CELL CONTENTS The cell contents of the plant are divided into two groups: first, organic cell contents; and secondly, inorganic cell contents. The =organic= cell contents include plastids, starch grains, mucilage, inulin, sugar, hesperidin, alkaloids, glucocides, tannin, resin, and oils. CHLOROPHYLL