THE CELL AND TISSUE. 



63 



be profitably studied. The work can be made much more valuable, if a 

 compound microscope can be used for the exhibition of prepared mounts that 

 illustrate the parts of the cell, the cell-contents and the various kinds of 

 tissue, etc. 



2. The cells in the tissues of common plants are, with few 

 exceptions, microscopic in size. The majority of them are 

 between one-hundredth and one-thousandth of an inch in 

 diameter. In bast tissue they are much larger. Plant hairs 

 often consist of a single cell and are usually large enough 

 to be detected by the unaided eye. Sometimes they are very 

 long, as some Algse, the milk-vessels in some Spurges, and the 

 cotton, which consists of unicellular hairs from the seeds of 

 the Cotton-plant. Many cells, on the other hand, are extremely 

 small. The unicellular plants called Yeast and Bacteria are 

 examples of such. The transparent, nearly round Yeast-cells 

 are about three ten-thousandths of an inch in diameter. The 

 Bacterium termo, or common fungus which causes putrefaction, 

 consists of a cell about nine hundred-thousandths of an inch 

 long and little more than half as wide. 



3. The vegetable cell usually consists of four parts which 

 are readily distinguishable, namely, protoplasm, nucleus, cell- 

 wall and cell-sap (Fig. 95). The Protoplasm is a nearly 



Nucleus 



Protoplasm 



Fig. 95. 



Fig. 96. 



transparent, more or less granular, usually semifluid sub- 

 stance. A denser small globular portion within, called the 

 nucleus, is usually visible. The protoplasm is the essential 

 part of the cell. In it, all the vital activities are manifest and 



