PROTOPLASM AND PLANT-0BLL8. 9 



(e) Make longitudinal sections of a stem of Indian corn, so as to 

 obtain very thin slices of some of the threads which run lengthwise 

 through it. Cell-walls showing rings, spirals, and reticulations may 

 be readily found (Fig. 5). 



(/) Mount spores of the "black rust" of wheat or oats (by care, 

 rully scraping off one of the blackish spots on the stem or leaves) for 

 examples of cell-walls thickened for protection. 



{g) Mount pollen-grains of mallows or squashes for thickened 

 wall which has developed projections externally. 



(A) Make longitudinal sections of the fibrovascular bundles of 

 squash-stems for examples of sieve-vessels showing the continuity of 

 the protoplasm through the cell-walls. 



{i) For large cells examine the parts (leaves and stems) of water- 

 plants. In the Water-net (Hydrodictyon) they may be seen with the 

 naked eye. 



(j) For very small cells mount a minute drop of putrid water and 

 examine with the highest power of the microscope available. Myri- 

 ads of minute cells, each a single plant, will be seen darting hither 

 and thither in the water. These are the Bacteria, to be more fully 

 noticed in Chapter VII. A tumbler in which leaves and twigs have 

 been allowed to begin to decay will furnish good material. 



(Jc) For Green Slime scrape ofE a little of the green, slimy growth 

 to be found on damp walls, rocks, etc. Under a high power many 

 little green balls of protoplasm may be observed. Each has a cell- 

 wall. 



13. How New Cells are Formed. — Most plant-cells in 

 some stage of their growth are capable of producing new 

 cells. This power is mostly confined to their early thin- 

 walled state, new cells being rarely formed after the walls 

 have attained any considerable thickness. There are two 

 principal methods, viz., (1) by the Division of cells, (2) by 

 the Union of cells. 



14. In some cases of Division the cell simply constricts 

 its sides so as to pinch itself into two parts. In other 

 cases the protoplasm first divides itself through the middle, 

 and the two halves then help to form a partition-wall of 

 cellulose between them. Both of these modes of division 

 are known as Fission. 



