THE CELL AND TISSUE. 67 



starch is examined under the microscope a nucleus is seen in 

 the larger grains and around it are numerous concentric layers. 

 Starch after its formation in the chlorophyll becomes dissolved, 

 and is transported to growing parts and at once consumed in 

 the formation of the vegetable fabric ; or it reappears in the 

 form of starch in reservoirs, stored up for future use, as in 

 seeds, tubers, bulbs, roots, stems, etc. Other products are 

 formed in cells, as oils, organic acids, alkaloids, resins, salts, 

 sugars, etc. 



Scrape the freshly cut and moist surface of a potato, bean or grain of wheat 

 or com and a quantity of starch will be obtained. Add to it a drop of 

 dilute iodine solution (made by dissolving a bit of potassium iodide in a little 

 water and adding a very small grain of metallic iodine, till a cherry-red 

 solution is obtained) and note the deep-blue coloration. This is the test for 

 the presence of starch. Examine also with the lens. Make with a sharp 

 blade very thin slices of various tissues, as potato-tuber, bean, twigs, etc., 

 put them under the lens and then add a little of the iodine solution. Some- 

 times the stem of the Oxalis, Begonia or other plants have also crystals that 

 can be seen with the lens when very thin sections are examined. 



8. Though each plant begins its existence as a single cell, 

 or simple mass of protoplasm in the embryo cell, all but the 

 unicellular species very soon become many-celled. This mul- 

 tiplication of cells is brought about by the division of the first 

 cell into two. Each of these after increasing in size divides 

 into two, or four in all. The resultant four divide into eight 

 and so on indefinitely. A microscopic study of the process 

 of division shows it to be very complicated, and its elucida- 

 tion will not be attempted here. Suffice it to state that the 

 nucleus takes the initiative ; after it divides into two portions, 

 the protoplasm becomes separated into two masses, a new cell- 

 wall being formed between them and two distinct cells are 

 the result. The increase in the size of plants is then due to 

 an increase in the number of cells. Countless millions are to 

 be found even in a plant of moderate size. It has been de- 

 monstrated that though the protoplasm is surrounded in each 

 case, and apparently isolated, by a cell-wall, yet minute pro- 

 toplasmic tlireads reach from each mass through the walls to 



