46 



HUTCHINSON'S POPULrAB, BOTANY 



FIG. 70. COMMON BEET (Beta vulgaris). 



giving a yellow or yellowish brown 

 instead of a blue colour with iodine, 

 and by its inalterability under the 

 influence of ferments. It assumes 

 ^ e f orm f beautiful sphere-crys- 

 tals on tne addition of alcohol, 

 and is coloured an orange-red with 

 alcoholic solution of orcin, after 

 warming with hydrochloric acid. 



An earlier occasion should per- 

 haps have been chosen to speak 

 of the sap of plants. We propose 

 in the following section to treat of 

 its composition only, reserving a 

 consideration of its functions for 

 future chapters. Cell-sap is the 



fluid which the roots of plants absorb from the soil, or the leaves from the 

 atmosphere, and which contains in solution the true nutritious principles. 

 Water is the chief constituent of cell-sap, calculations showing that for 

 every two hundred grains of water absorbed and exhaled by a plant, 

 only one grain of inorganic matter is appropriated ; and for every two 

 thousand grains of water consumed, one grain of inorganic matter is 

 appropriated. 



Young cells are usually well supplied with sap, which fills the spaces 

 (called vacuoles) occurring in the protoplasm. It is conveyed into the plant 



by the roots, but not till it reaches 

 the leaves does it undergo any im- 

 portant changes. The proof of 

 this must be left for another 

 chapter, our present purpose being 

 simply to speak of the sap as a 

 substance found in vegetable cells 

 apart from the functions which 

 it discharges. Cell-sap may be 

 sweet or acid, clear or turbid, 

 nutritious or innutritions, so that 

 its value from an economic point 

 of view is often great. The re- 

 freshing acid taste of most unripe 

 fruits is due to the sap. Citric 

 acid a familiar form of it gives 

 sharpness to the juices of lemons, 



FIG. 71. ANTS HELD FAST BY THE MILK-SAP oranges, limes, and many of our 

 OF THE GARDEN LETTUCE. commonest fruits, as the cranberry, 



