114 



PART II. THE INTIMATE STRUCTURE OF PLANTS. 



[26. 



nitrogenous substances such as asparagin. It very commonly is 

 rich in sugar ; either grape-sugar (C 6 H 12 O 6 ), as in the grape and 

 other fruits, and in fact most parts of plants at particular times ; 

 or cane-sugar (C^H^On) as in the Sugar-cane, the Maple, and the 

 Beetroot. In some plants (e.g. Jerusalem Artichoke, Dahlia, Globe 

 Artichoke) the cell-sap is rich in inulin, a substance having the 

 same percentage composition as starch (represented by formula 

 C 6 H 10 5 ) : when a portion of tissue, of one of these plants, such as 

 a piece of the tuberous root of the Dahlia, is kept in spirit, the 



inulin slowly precipitates in 

 the form of sphoerocrystals 

 (Fig. 73) adhering to the walls. 

 The cell-sap also very fre- 

 quently holds colouring-mat- 

 ters in solution ; for instance, 

 the colouring-matters of most 

 red and blue flowers (erythro- 

 phyll and anthocyanin) ; of 

 many fruits, such as the 

 Cherry and Elderberry; of 

 "copper leaves," such as those 

 of Copper Beech and Hazel, 

 and of the Beet-root. 



26. Cell-Formation. 

 The formation of a cell is ne- 

 cessarily dependent upon a 

 pre-existing cell ; the direct 

 development of a cell from the 

 necessary chemical substances 

 that is, spontaneous genera- 

 tion has not yet been ob- 

 served. Moreover, it can only 

 take place when the protoplasm concerned is in the embryonic con- 

 dition ; as, for instance, in growing-points, germinating spores, etc. 

 Cell-formation consists essentially in the reorganisation of the 

 protoplasmic unit (energid, p. 90) or units in which it occurs ; it 

 may take place about one centre, or, more frequently, about two or 

 more centres, with consequent multiplication of cells. Hence, cell- 

 formation does not necessarily involve a multiplication of cells, 

 still less a formation of cell-walls ; it necessarily involves the 

 formation of a new cell, 



FIG. 73. Sphserocrystals of inulin in the 

 tissue of the tuberous root of Dahlia variabilis 

 after prolonged action of alcohol. (After 

 Strasburger : x 240.) 



