Increase of Cells., 



great quantities of these cells, and not bv the mere expansion of 

 a few original cells, it becomes a question of great interest to 



Fig. C. 





a 



Perpendicular slice of tlie leaf of the Cay-Laurel ; <i, ft', the sliin of the upper and lower surfaces ; 

 6, a rib running through the spongy substance. Magnified 200 diameters. 



know how those cells increase in number in the growth of plants. 

 Our little Prot.ococciis^ or green dust, will furnish us Avith useful 

 information here. Most of the cells, examined with a high 

 mafrnifying power, will be found to exhibit an appearance 

 differing a little from the simplest state above described. They 

 will exhibit various stages of the increase of these cells. They 

 will be found to display a more or less distinct line extending 

 across and cutting thetn into halves, or two lines, crossing- one 

 another, and thus cutting the cells into quarters (fig. 5). These 

 are true divisions, and by watching the progress of growth we find 

 that the cells do becomt; really divided in these lines, and that four 

 cells are thus formed from each, these four at length sey)arating 

 nnd growing up by degrees to the size of the parent. This in- 

 crease of size begins before they have separated from each otlier, 

 so that tiie groups of four imperfectly divided cells are alwavs 

 larjrer than the singh^ cells. 



The increase in this case ends directly in the increase of the 

 iiuml)er of sejiarate individuals, but it is evident that if the four 

 cells remained adherent together, and swelled and divided again 

 in the same manner, and went on repeating the process, the mass 

 of cells might continue to increase in size up to anv degree, and, 

 moreover, it is clear that the larger the mass the more quickly it 



