30 



THE ELEMENTARY STRUCTURE OF PLANTS. 





SI 



Oq 

 1 o o 





!il?=o, 











5^ 



22 





and of the four in Fig. 18, forms a part of the thickness of the 

 coat of each, or is destroyed by the distention, or else (as in the 

 present instance) is dissolved into a jelly A slight modification of 

 this process occurs in 



36. Free Cell-Multiplication within 



a Motlicr-Cell, wliich is intermediate 

 in character between original cell- 

 formation and ordinary cell-multi- 

 plication. Here tlie whole contents 

 of a living cell, by constriction or 

 infolding of the primordial utricle, 

 divide into two or four parts (as 

 in Fig. 81 -83), and these may be 

 again divided; — each portion has 

 J|^| a coat of cellulose deposited over 

 its surface, and thus so many sep- 

 arate cells are produced, lying loose 

 in the cavity of the mother-cell, whose thin and 

 now dead cellulose-wall, which is all that is left of 

 it, usually disappears sooner or later, or is broken 

 up by the growth of the new crop of cells within. 

 In this way are formed the grains of pollen in the 

 anther, and the spores, or bodies Avhicli answer to 

 seeds, in the higher grades of Flowerless Plants. 



37. Ceil-Gl'OWlil. By appropriating assimilated 

 matter, the young cell increases in size until it 



20 



attains its full growth ; its walls, as they expand 

 and enclose a greater space, not diminishing, but rather increasing" 

 in tliickness. Therefore it not merely enlarges, but grows. If it 

 grows equally in all directions, and is not pressed upon on any side, 

 it keeps a spherical form ; if it grows more in one direction than in 

 any other it becomes oblong or cylindrical. In this way a cell is 

 sometimes drawn out into a slender tube ; of which the fibres of 

 cotton, and the cells of fibrous bark (Fig. 49) are good examples. 

 In the simplest plants, cells sometimes continue to elongate almost 



IM 



FIG 20. The branching summit of a plantlet of Conferva glomerata, magnified ; after 

 Mohl. The plant consists of a row of cells, filled with green grains floating in liquid : the 

 long cell at the upper end is seen in the process of dividing into two, at a, by constriction of 

 the primordial utricle. 



PIG. 21. A portion of the same at a, more magnified, showing the formation of the par- 

 tition. 22. Same, with the partition completed. 



