16 



ESSENTIALS OF BOTANY 



19. Microscopical Examination of Starch.' — Examine starch in 

 water with a rather high power of the microscope (not less than 200 

 diameters). 



Pulp scraped from a potato, that from a oanna rootstock, wheat 

 flour, the finely powdered starch sold under the commercial name of 

 " cornstarch " for cooking, oatmeal, and buckwheat finely powdered 

 in a mortar, will furnish excellent examples of the shape and mark- 

 ings of starch grains. Sketch all of the 

 kinds examined, taking pains to bring out 

 the markings.^ Compare the sketches 

 with Figs. 7 and 8. 



With a medicine-dropper or a very 

 small pipette run a drop of iodine solu- 

 tion under one edge of the cover-glass, 

 at the same time withdrawing a little 

 water from the margin opposite by touch- 

 ing to it a bit of blotting paper. Exam- 

 ine again and note the blue coloration of 

 the starch grains and the unstained or 

 yellow appearance of other substances 

 in the field. Cut very thin slices from 

 beans, peas, or kernels of corn ; mount in water, stain as above 

 directed, and draw as seen imder the microscope. Compare with 

 Figs. 7 and 8.^ Note the fact that the starch is not packed away in 

 the seeds in bulk, but that it is enclosed in little chambers or cells. 



Fig. 7. Canna Starch. 

 (Magnified 300 diameters.) 



20. Plant-Cells. — Almost all the parts of the higher 

 plants are built up of little separate portions called cells. 

 The cell is the unit of plant-structure, and bears something 



i At this point the teacher should give a hriet illustrated talk on the con- 

 struction and theory of the compound microscope. 



2 The markings will be seen more distinctly if care is taken not to admit 

 too much light to the object. Rotate the diaphrrigra beneath the stage of the 

 microscope, or otherwise regulate the supply of light, until the opening is 

 found which gives the best effect. 



3 The differentiation between the starch grains, the other cell-contents, 

 and the cell-walls will appear better in the drawings if the starch grains are 

 sketched with blue ink. 



