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Fig. 122.—To show the Escape of Oxygen.
covered area. 88. Plants or parts of plants that have developed
no chlorophyll can form no starch. Secure a variegated leaf of
coleus, ribbon grass, geranium, or of any plant showing both white
and green areas. On a day of bright sunshine, test one of these
leaves by the alcohol and iodine method for the presence of starch.
Observe that the parts devoid of green color have formed no
starch. However, after starch has once been formed in the leaves,
it may be changed into soluble substances and removed,
to be again converted into starch in certain other parts of
the living tissues. To test the giving off of oxygen by day.
89. Make the experiment illustrated
in Fig. 122. Under a funnel
in a deep glass jar containing
fresh spring or stream water place
fresh pieces of the common
waterweed elodea (or anacharis).
Have the funnel considerably
smaller than the vessel, and support
the funnel well up from the
bottom so that the plant can more
readily get all of the carbon dioxid
available in the water. Why would
boiled water be undesirable in this
experiment? For a home-made
glass funnel, crack the bottom off
a narrow-necked bottle by pressing
a red-hot poker or iron rod
against it and leading the crack
around the bottle. Invert a test-tube
over the stem of the funnel.
In sunlight bubbles of
oxygen will arise and collect in
the test-tube. If a sufficient
quantity of oxygen has collected,
a lighted taper inserted in the
tube will glow with a brighter flame, showing the presence of
oxygen in greater quantity than in the air. Shade the vessel.
Are bubbles given off? For many reasons it is impracticable
to continue this experiment longer than a few hours. 90. A
simpler experiment may be made if one of the waterweeds
Cabomba (water-lily family) is available. Tie a lot of branches
together so that the basal ends shall make a small bundle. Place
these in a large vessel of spring water, and insert a test-tube of
water as before over the bundle. The bubbles will arise from the
cut surfaces. Observe the bubbles on pond scum and waterweeds
on a bright day. To illustrate the results of respiration
