SUGGESTIONS.—_To test for chlorophyll._ =84.= Purchase about a gill of wood alcohol. Secure a leaf of geranium, clover, or other plant that has been exposed to sunlight for a few hours, and, after dipping it for a minute in boiling water, put it in a white cup with sufficient alcohol to cover. Place the cup in a shallow pan of hot water on the stove where it is not hot enough for the alcohol to take fire. After a time the chlorophyll is dissolved by the alcohol which has become an intense green. Save this leaf for the starch experiment (Exercise 85). Without chlorophyll, the plant cannot appropriate the carbon dioxide of the air. _Starch and photosynthesis._ =85.= Starch is present in the green leaves which have been exposed to sunlight; but in the dark no starch can be formed from carbon dioxide. Apply iodine to the leaf from which the chlorophyll was dissolved in the previous experiment. Note that the leaf is coloured purplish-brown throughout. The leaf contains starch. =86.= Secure a leaf from a plant which has been in the dark for about two days. Dissolve the chlorophyll as before, and attempt to stain this leaf with iodine. No purplish-brown colour is produced. This shows that the starch manufactured in the leaf may be entirely removed during darkness. =87.= Secure a plant which has been kept in darkness for twenty-four hours or more. Split a small cork and pin the two halves on opposite sides of one of the leaves, as shown in Fig. 120. Place the plant in the sunlight again. After a morning of bright sunshine dissolve the chlorophyll in this leaf with alcohol; then stain the leaf with the iodine. Notice that the leaf is stained deeply except where the cork was; there sunlight and carbon dioxide were excluded, Fig. 121. There is no starch in the 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 colour 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 the carbon dioxide available in the water. Why would boiled water be undesirable in this experiment? For a home-made glass funnel, crack