compared with those of animals. 55 



2. Formation op cells by division. 



This mode of cell-multiplication is probably that which 

 presents itself most frequently to the obseryer. It may 

 be studied to the greatest advantage in that common green 

 thread-like vegetation known to botanists as Confervse, 

 which is found in the beds of rivulets attached to their 

 stones and pebbles, and which invariably shows itself on 

 the surface of rooks whenever the water which flows over 

 them is exposed to the action of light. This matter, ex- 

 amined with the microscope, presents to the eye a longi- 

 tudinal series of cells which are produced by merismatio 

 division in the following manner : — 



The primordial utricle or inner wall of the cell is in- 

 fl.eoted towards its middle part. This inflection, at first 

 a little salient, insensibly increases until finally the two in- 

 flected walls meet in the centre of the cell, and form a 

 complete partition across its cavity, so that in the place of 

 one we have two cells. These dilate and subdivide again 

 in the same manner, and in this way a linear series of cells 

 is produced, when the subdivision of them takes place in 

 one direction, or .a plane or solid mass of cells when it 

 takes place in two or more directions. The endoohrome of 

 the primary cell, is necessarily separated into two halves by 

 the formation of the septum, and is again subdivided with 

 every repetition of the process,- so that all the cells contain 

 a separate portion of it. The contiguity of the cells blends 

 together the hues of their separate endoohromes, and gives 

 an evenly difi'used color to the surface of the tissues. 



These fresh water confervas illustrate the vegetative pro- 

 cess in more highly organized plants, which acquire their 

 complex structure from equally simple beginnings. Hence 

 it is not original cell-formation so much as the multiplica- 



