PLANT STRUCTURE 133 



bination of minute chambers which are called cells. It 

 became known that there are many low forms of plant life 

 which consist of but a single cell. A study of these re- 

 vealed the fact that within this individual cell lay the 

 vital element which is known as life. 



104. Cell characters. In 1846 Mohl of Tubingen, in 

 his study of the cell, gave to the contents of this cell the 

 name of protoplasm. It was discovered that this proto- 

 plasm would exist for a time under certain conditions 

 without any special envelope or protective covering. As 

 a rule, however, it secretes at once a firm outer coat and so 

 builds for itself a dwelling house. This is now called the' 

 cell wall. The cell wall with the protoplasm which it con- 

 tains is known as the unit of plant structure, and every 

 plant culturist in dealing with the whole plant should 

 recognize the importance of this individual part. 



The microscope reveals the fact that this protoplasm is 

 not simply a mass of semi-fluid, more or less transparent, 

 but it has definite directions of circulation, and within it 

 are bodies of definite shape and size. One distinct body 

 exists in all cells, and to this is given the name of the 

 nucleus. Other more or less transparent bodies are dis- 

 cerned, and these are called plastids, or protoplasts. 

 When they are perfectly white, they are called leuco- 

 plasts, when green, they are termed chloroplasts, and 

 when red, chromoplasts. The predominance of these 

 different colored atoms gives characteristic colors to the 

 cells. The importance of them in plant growth will be 

 noticed later. 



105. Cell arrangement. Low forms of plants which 

 consist of biit a single cell are, for the most part, nearly 

 spherical. Higher forms of plant life begin their exist- 

 ence as a single cell, but have the power of cell division, 



