CHAPTER II. THE FORMATION OF CELLS. 



147 



Apply the following tests to determine the nature of the crystals : 

 Acetic acid has no effect on silica and calcium oxalate, but calcium carbo- 

 nate dissolves with effervescence. Hydrochloric acid has no effect on silica, but 

 dissolves calcium oxalate without effervescence, and calcium carbonate with 

 effervescence. 



Make careful drawings of the different forms of crystals which you observe. 



CHAPTER II.— THE FORMATION OF CELLS.— PLANT 



TISSUES. 



Most cells have the power of reproduction, or of giving origin 

 to new cells. This may take place in one of three principal ways: 

 By division, by rejuvenescence, and by union. 



1. TJie Division of Cells. There are three different ways in 



which this may take 

 place. The most 

 common mode is by 

 fission, or the sepa- 

 ration of the cell into 

 two equal portions. 

 This may occur in 

 either of the two fol- 

 lowing ways : 



a. A constriction 

 may take place in 

 the middle of the 

 cell, and, along the 

 plane of this con- 

 striction, the cell- 

 wall may grow in- 

 ward until the cell 

 contents become separated into two equal portions. This mode 

 has been observed in some of the lower Algae, Fig. 388. 



b. A delicate partition of cellulose may at once be formed 

 through the middle of the cell. This is the usual mode by which 

 tissues are formed and growth takes place in all the higher 

 plants. It is illustrated in Fig. 391, which represents the grow- 

 ing embryo of the Onion. The terminal portion has just divided 

 into two cells, and these and the one below them are preparing 



Fig. 390. 



Fig. 



I A 



Fig. 390., a and b. — Earlier and later stages, respect- 

 ively, in the cell divisions of Spirogyra. Magnified about 

 500 diameters. 



Fig. 301. — Young embryo of the Onion, showing fission 

 of cells. Magnified about 400 diameters. 



