FORMATION OF NEW CELLS 19 



cated composition, usually bitter to the taste and very 

 frequently poisonous to animals. 



Laboratory Studies, (a) To show the large amount of 

 water in living cells place a few threads of pond-scum (Spiro- 

 gyra) in a little water and examine under the microscope. 

 Add a little strong glycerine which has a great avidity for 

 water. Note how the cells collapse as the water is withdrawn. 

 Repeat the experiment with thin sections of some herbaceous 

 stem or simply allow the latter to dry out in the air. 



(b) Taste the stem of sugar cane or growing Indian corn or a 

 piece of a sugar beet. The presence of sugar is readily recog- 

 nizable. Put small pieces of these plants into considerable 

 quantities of 95 per cent, alcohol to remove the water, or into 

 pure glycerine. The water is withdrawn rapidly by the 

 reagents and the cane sugar, which is practically insoluble in 

 them, crystallizes out in fine stellate crystals Sections for 

 examination must be mounted in the alcohol or glycerine as 

 water will redissolve the sugar. 



(c) Make thin sections of the root of Dahlia or sunflower 

 (Helianthus) that has been preserved in strong alcohol and 

 note the large sphaerocrystals of inulin. 



(d) To study glucose or fructose test the juices of various 

 fruits with Fehling's solution, which gives a precipitate of copper 

 oxide with both these sugars but not with cane sugar or inulin. 



(e) The presence of acids or acid salts is readily discernible 

 by the taste in many plants, e.g. stem of rhubarb, leaves of 

 Oxalis, fruit of lemon, cranberry, etc. In smaller quantities 

 it can be demonstrated by placing the cut surface of the tissue 

 to be tested in contact with a piece of blue litmus paper which 

 will be turned red by the action of acids. 



32. Formation of New Cells. No cell can originate 

 except from some pre-existing cell or cells. Most cells 

 are capable of producing new cells at some stage of their 

 development, but frequently the power is soon lost. 

 New cells arise either through the division of a cell or 

 through the union of two (or rarely more) cells. In the 

 cell formation by division we distinguish two types, each 



