=145. Chlorophyll is a pigment which resides in the chloroplast.=—That the chlorophyll is a coloring substance which resides in the chloroplastid, and does not form the body itself, can be demonstrated by dissolving out the chlorophyll when the framework of the chloroplastid is apparent. The green parts of plants which have been placed for some time in alcohol lose their green color. The alcohol at the same time becomes tinged with green. In sectioning such plant tissue we find that the chlorophyll bodies, or chloroplastids as they are more properly called, are still intact, though the green color is absent. From this we know that chlorophyll is a substance distinct from that of the chloroplastid. =146. Chlorophyll absorbs energy from sunlight for photosynthesis.=—It has been found by analysis with the spectroscope that chlorophyll absorbs certain of the rays of the sunlight. The energy which is thus obtained from the sun, called _kinetic_ energy, acts on the molecules of CH₂O₃, separating them into molecules of C, H, and O. (When the CO₂ from the air enters the plant cell it immediately unites with some of the water, forming carbonic acid = CH₂O₃.) After a series of complicated chemical changes starch is formed by the union of carbon, oxygen, and hydrogen. In this process of the reduction of the CH₂O₃ and the formation of starch there is a surplus of oxygen, which accounts for the giving off of oxygen during the process. =147. Rays of light concerned in photosynthesis.=—If a solution of chlorophyll be made, and light be passed through it, and this light be examined with the spectroscope, there appear what are called absorption bands. These are dark bands which lie across certain portions of the spectrum. These bands lie in the red, orange, yellow, green, blue, and violet, but the bands are stronger in the red, which shows that chlorophyll absorbs more of the red rays of light than of the other rays. These are the rays of low refrangibility. The kinetic energy derived by the absorption of these rays of light is transformed into potential energy. That is, the molecule of CH₂O₃ is broken up, and then by a different combination of certain elements starch is formed.[8] [8] In the formation of starch during photosynthesis the separated molecules from the carbon dioxide and water unite in such a way that carbon, hydrogen, and oxygen are united into a molecule of starch. This result is usually represented by the following equation: CO₂ + H₂O = CH₂O + O₂. Then by polymerization 6(CH₂O) = C₆H₁₂O₆ = grape sugar. Then C₆H₁₂O₆-H₂O = C₆H₁₀O₅ = starch. It is believed, however, that the process is much more complicated than this, that several different compounds are formed before starch finally appears, and that the formula for starch is much higher numerically than is represented by C₆H₁₀O₅.