74' BOTANY 



cytoplasm. No sharp distinction can, however, be drawn between 

 the sap cavity and vacuoles, and, moreover, a number of such vacuoles 

 may take the place of the sap cavity itself. The cell sap usually 

 gives an acid reaction, though in water-plants, according to Tschirch, 

 this reaction is often uncertain. The substances held in solution by 

 the cell sap are very various. The soluble carbohydrates, in parti- 

 cular the sugars, cane sugar, the glucoses, and especially grape sugar, 

 frequently occur in the cell sap. The glucoses may be recognised by 

 their reducing properties. 



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

 and, after being washed out, 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 same treatment gives only a blue colour to 

 the cell sap. 



Carbohydrates are transported in a plant principally in the form of 

 glucose ; cane sugar, on the contrary, is stored up as reserve material ; as 

 for example, in the sugar-beet, in the stems of sugar-cane, and in other 

 plants from which the sugar of economic use is derived. 



Inulin, a carbohydrate in solution in cell sap, takes the place of 

 starch in many orders of plants, as, for example, in the Compositae. 



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 sphserites, spheroidal bodies com- 

 posed of radiating crystal needles arranged in concentric layers. 



Aspakagin is also generally present in the cell sap. 



There are frequently found dissolved in the cell sap tannins, alkaloids, 

 and glucosides, such as coniferin, hesperidin, amygdalin, solanin, sesculin, 

 saponin 4 and also bitter principles related to the glucosides. It is also often 

 possible to detect in the cell, sap one of the benzole group, .phloroglucin, which in 

 the presence of hydrochloric acid, stains lignified cell walls a violet colour. Organic 

 acids are also of frequent occurrence in the cell sap ; thus, malic acid is usually 

 present in the leaves of the succulents. For the most part, these organic acids 

 unite with bases, and the salts which are formed often crystallise. Of acid salts 

 which are less frequent than free acids, the binoxalate of potassium found in 

 Field Sorrel (Bumex) and "Wood Sorrel (Oxalis) deserves special mention. 



The cell sap is often coloured, principally by the so-called antho- 

 CYANIN. This is blue in an alkaline, and red in an acid reactino- cell 

 sap, and, under certain conditions, also dark red, violet, dark-blue and 

 even black. Blood-coloured leaves, such as those of the Purple Beech 

 owe their characteristic appearance to the united presence of green 

 chlorophyll and anthocyanin. The different colours of flowers are due 

 to the varying colour of the cell sap, to the different distribution of the 

 cells containing the coloured cell sap, and also to the different combina- 

 tions of dissolved colouring matter with the yellow, yellowish red or 



