148 



PHYSIOLOGICAL BOTANY. 



some cases to determine with accuracy their chemical 

 constituents. 



376. Cell-sap is the watery fluid in the cell which 

 suspends the food and working material taken into 

 the cell from the air and the 



soil and the soluble substances 

 which the plant produces, and 

 is the medium by which food is 

 conveyed throughout the plant's 

 structure. All parts of the active 

 cell are filled with water ; it con- 

 stitutes a large part of the cellu- 

 lose, and forms the greater part 

 of the bulk of protoplasm. Sugar 

 is a prominent sub- 

 stance in the cell- 

 sap, both cane and 

 grape. Cane-sugar 



flhnnnHcj in thp pplla 475, 4, cross-section of oak-gall ; d, sclerenchymatons cells ; 



3 c, outside tissue, with oxalate crystals , e, inner tissue containing 



of Sugar Cane, Sugar 8tarch and resin ' * forms of calcium oxalate crystals ' 

 Maple, Beet, Sorghum, Indian Corn, and most of the 

 higher plants ; while grape-sugar gives sweetness to 

 grapes, cherries, figs, and gooseberries. In the poma- 

 ceous and drupe fruits both kinds are present. For cell- 

 sap in both large and small vacuoles, see Fig. 466, p; 

 Fig. 467, B, 8, 8, s. 



377. New cells, to which the enlargement or growth 

 of the plant is due, are formed in one of the three fol- 

 lowing typical modes : 



378. 1, Rejuvenescence. In this method of pro- 

 ducing new cells, the entire mass of the protoplasm is 

 expelled from the old cell, and, when set free, sur- 

 rounds itself with a wall, thus becoming a new cell. 



