68 PHYSIOLOGY. 



162. Starch grains formed in the ehloroplasts. — During carbon conver- 

 sion the starch formed is deposited generally in small grains within the green 

 chloroplast 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 ehloroplasts 

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

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

 but which has passed in solution. Thus the functions of the chloroplast are 

 twofold, that of the conversion of carbon and the formation of starch grains. 



163. In the translocation of starch when it becomes stored up in various 

 parts of the plant, it passes from the state of solution into starch grains in 

 connection with plastids similar to the ehloroplasts, but which are not green. 

 The green ones are sometimes called chromoplasts, while the colorless ones 

 are termed leucoplasts. 



164. Carbon conversion in other than green plants. — While organic com- 

 pounds are usually only formed by green plants, there are some exceptions. 

 Apparent exceptions are found in the blue-green alga? like oscillatoria, 

 nostoc, or in the brown and red sea weeds like fucus, rhabdonia, etc. These 

 plants, however, possess chlorophyll, but it is disguised by another pigment or 

 color. There are plants, however, which do not have chlorophyll and yet 

 form organic substance with evolution of oxygen in the presence of light, as 

 for example a purple bacterium, in which the purple coloring substance 

 absorbs light, though the rays absorbed most energetically are not the red. 



165. Influence of light on the movement of chlorophyll bodies. — In fern 

 prothallia. — If we place fern prothallia in weak light for a few hours, and 

 then examine them under the microscope, we find that the most of the chloro- 

 phyll bodies in the cells are arranged along the inner surface of the 

 horizontal wall. If now the same prothallia are placed in a brightly lighted 

 place for a short time most of the chlorophyll bodies move so that they are 

 arranged along the surfaces of the perpendicular walls, and instead of having 

 the flattened surfaces exposed to the light as in the former case, the edges 

 of the chlorophyll bodies are now turned toward the light. (See figs. 

 56, 57.) The same phenomenon has been observed in many plants. Light 

 then has an influence on chlorophyll bodies, to some extent determining their 

 position. In weak light they are arranged so that the flattened surfaces are 

 exposed to the incidence of the rays of light, so that the chlorophyll will 

 absorb as great an amount as possible of kinetic energy; but intense light is 



hydrogen, and oxygen are united into a molecule of starch. This result is 

 usually represented by the following equation: C0 2 -f- H 2 = CH a O -|- O a . 

 Then by polymerization 6(CH u O) = C G H 12 6 = grape sugar. Then 

 C 6 H 12 0j — H 2 = C„H l0 O = starch. It is believed, however, that the 

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

 pounds are formed before starch finally appears. 



