1896. 1 3IICR0SC0PICAL JOURNAL. 263 



through with the microscope, it eau be cut with a razor 

 or very sharp scapel, the blade well flooded with water. 

 Cut a number of sections to get practice, and float them 

 as cut into a watch-glass, taking to care that you are 

 able to recognize the exact location of the parts of the 

 section in the potato. Select the thinnest and transfer 

 it to the center of a slide, examine it uncovered 1. p. to 

 recognize its parts and draw, then cover it with strong 

 iodine solution and let it stand for several minutes. Now 

 wash out all the iodine that will come away, add a drop 

 of water and cover and examine with the low power. 

 You will now find that the parenchyma is all stained 

 blue, while bark and the fibro-vascular tissue are colored 

 brown. Iodine stains starch blue, while it stains cellu- 

 lose and protoplasm brown, thus you learn tliat the 

 parenchyma is largely starch. Examine the diff"erent 

 parts of the section with the higher power, noting that 

 starch is in oval grains and embraced by a net-work of 

 cell-walls, which stains with the iodine with difficulty, 

 they are composed of the substance cellulose', (where 

 the starch grains are not inside of cells, it is because 

 they have escaped in the process of making the section.) 

 Examine the cells in the level of the bark and see that 

 some of them are deeply stained brown, note their shape 

 and position, distance from the surface and from the 

 parenchyma, note in some the more densely stained, round 

 nucleus, and search for some in which a few grains of starch 

 can be seen in process of formation, determine their 

 exact location in the cell and draw them. Examine also 

 the fibro-vascular tissue and distinguish certain spiral 

 structures ; they are cells which have thickened walls 

 used for support. 



If it is desired to do so you can preserve the section 

 temporarily by draining off" as much as much as possible of 

 the water and replacing it with glycerine; or a more per- 



