THE STRUCTURE OF PLANTS 



29 



protoplasm 

 of cell-body 



i 



cell- 

 wall 



chlorophyll bodies, and show by arrows the direction 

 of their movements. 



6. (Demonstration.) Examine with the low power of the 

 microscope the sections of root, stem, and leaf, or 

 study Figures 11, 12, 15, 22. What have you learned 

 of the microscopic structure of root, stem, and leaf ? 



(Optional.) Make a drawing of four or five cells from 

 each of the organs studied. 



42. Cells and protoplasm. Under the microscope cells 

 at first appear to be only plane surfaces surrounded by lines. 

 In reality, however, each cell has 

 not only length and breadth, but 

 also thickness, and each cell is 

 covered on all sides by a cell-wall 

 which is composed of a lifeless 

 substance known as cellulose. 

 This wall is often so transparent 

 that we can look through it and 

 see the cell-body and nucleus 

 within (Fig. 6). 



The discovery of these minute 



bodies of which organs are com- ce ii. n ucieus 



posed was not made until about 

 the middle of the last century 

 (1838). With the rather imper- 

 fect microscopes then in use the 

 two discoverers, Schleiden and 

 Schwann, could see the cell -walls 

 only, and they did not know, as 

 we now know, that the most im- 

 portant part of the cell is not the lifeless wall of cellulose, 

 but the living substance which is found inside the cell-wall, 

 making up a large part of the cell-body and cell-nucleus. 



FIG. 6. Plant cell. The spaces 

 in the cell-body are filled with 

 cell-sap. 



