70 PHYSIOLOGY. 



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 chloro- 

 plastids 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 fir photosynthesis. It 

 has been found by analysis with the spectroscope that chlorophyll absorbs cer- 

 tain of the rays of the sunlight. The energy which is thus obtained from 

 the sun, called kinetic energy, acts on the molecules of CH 2 O 3 , separating 

 them into molecules of C, H, and O. (When the CO 2 from the air enters 

 the plant cell it immediately unites with some of the water, forming carbonic 

 acid = CH 2 O 3 .) After a series of complicated chemical changes starch is 

 formed by the union cf carbon, oxygen, and hydrogen. In this process of 

 the reduction of the CH.,O 3 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 

 CH 2 O 3 is broken up, and then by a different combination of certain elements 

 starch is formed.* 



148. Starch grains formed in the chloroplasts. During photosynthesis the 

 starch formed is deposited generally in small grains within the green chloro- 

 plast in the leaf. We can see this easily by examining the leaves of some 

 moss like funaria which has been in the light, or in the chloroplasts of the 

 prothallia of ferns, etc. Starch grains may also be formed in the chloro- 

 plasts from starch which was formed in some other part of the plant, but 



* In the formation of starch during photosynthesis the separated mole- 

 cules 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: CO 2 +H 2 O = CH 2 O + Oj. 

 Then by polymerization 6(CH 2 O) = C 8 H 12 O 8 = grape sugar. Then 

 Cfi H iAi H 2 O = C 6 H,.O 5 = starch. It is believed, however, that the 

 process is much more complicated than this, that several different com- 

 pounds are formed before starch finally appears, and that the formula for 

 starch is much higher numerically than is represented by C 8 H 10 O . 



