28 BOTANY 



are of great value in the life of the plant as RESERVE MATERIALS. 

 They are accumulated in considerable quantity for future use in the 

 cells of storage organs (bulbs, tubers, seeds). Others are end products 

 of metabolism which may, however, be of great ecological importance. 



A. Inclusions of the Cytoplasm 



1. Fluid Inclusions of the Cytoplasm, (a) The Cell Sap. This 

 name is given to the watery fluid in the larger vacuoles or the single 

 sap cavity of vegetable cells (Fig. 3). It is more or less rich in 

 various dissolved substances, which are sometimes reserve materials 

 and at others end products of metabolism ; solid inclusions, especially 

 in the form of crystals, also occur in it. The substances in the cell 

 sap may be the same or different from those in the protoplasm. The 

 dissolved substances may differ in the various vacuoles of the 

 same cell. 



All cell sap contains in the first place INORGANIC SALTS, especially 

 nitrates, sulphates, and phosphates. Its reaction is usually acid owing 

 to the presence of ORGANIC ACIDS (e.g. malic acid, which is constantly 

 present in the leaves of succulent plants, tartaric acid, oxalic acid, etc.), 

 or salts of these. 



The SOLUBLE CARBOHYDRATES are especially important constituents 

 of the cell sap, often as reserve materials. Various SUGARS (cane-sugar, 

 maltose or malt-sugar, glucose or grape-sugar) are the most important. 

 Cane-sugar is frequently stored as a reserve material, as in the sugar- 

 beet, carrot, the stem of the sugar-cane, and other plants from which 

 sugar is obtained. A similar place is taken by the carbohydrate 

 INULIN in the Compositae and by GLYCOGEN in the Fungi. Carbo- 

 hydrates are transported throughout the plant in the form of sugar. 



If preparations containing glucose be placed in a solution of copper sulphate, and, 

 after being thoroughly washed, are transferred to a solution of caustic potash and 

 heated to boiling, they will give a brick-red precipitate of cuprous oxide. If cane- 

 sugar or saccharose be present, this treatment gives only a blue colour to the cell 

 sap. Treated with alcohol, inulin is precipitated in the form of small granules, 

 which may be redissolved in hot water. When portions of plants containing much 

 inulin, such as the root tubers of Dahlia variabilis, are placed in alcohol or dilute 

 glycerine, the inulin crystallises out and forms sphaerites, spheroidal bodies com- 

 posed of radiating crystal needles ; these sphere - crystals often show distinct 

 stratification and are easily broken up into wedge-shaped portions. 



GLYCOGEN, which is of frequent occurrence in animal tissues, occurs in the 

 Fungi, Myxomycetes, and the Cyanophyceae in the form of droplets. In the 

 Fungi it takes the place of other carbohydrates such as starch and sugar. 

 Cytoplasm containing glycogen is coloured reddish -brown with a solution of 

 iodine. This colour almost wholly disappears if the preparation be warmed, but 

 reappears on cooling. 



MUCILAGE is often found in the cells of bulbs, as in Allium cepa and Urginea 

 (Sdlla) maritima ; in the tubers of Orchids ; also in aerial organs (Fig. 22), especially 



