16 ESSENTIALS OF BOTANY 
19. Microscopical Examination of Starch.1— 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 canna 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 under the microscope. Compare with 
Figs. 7 and 8.5 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. 
Fie. 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 
1 At this point the teacher should give a brief 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 diaphragm beneath the stage of the 
microscope, or otherwise regulate the supply of light, until the opening is 
found which gives the best effect. 
8 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. 
