WORK OF LEAVES: PHOTOSYNTHESIS 103 



result can be seen from the following simple formula: Grape 

 sugar, C 6 H 12 O 6 H 2 O = C 8 H 10 O 5 ,* which is the symbol for 

 starch. In many plants the sugar formed in the leaves does not 

 change to starch except that which is stored in the seed, as in field 

 corn, wheat, barley, etc. Sugar is found throughout other parts 

 of the plant, and we have seen that it is stored in quantity in the 

 sugar beet. In some plants it is not even changed to starch in 

 the seed, as in the sweet corn. In many plants, however, it is 

 changed to starch in the leaf very soon after its formation in the 

 leaf, as in most dicotyledons. 



171. Where the starch grains are first formed. The sugar 

 is dissolved in the cell sap, but the starch is deposited in grains. 

 These grains of starch at the time of their formation are deposited 

 in the chlorophyll bodies. Each grain begins as a very small body 

 and increases in size. (For translocation and storage of starch, 

 see Chapter XIV.) 



172. Photosynthesis takes place only in chlorophyll-bear- 

 ing plants and in the chlorophyll-bearing parts. Plants which 

 have been grown in the dark lack chlorophyll, f When brought 

 into the light photosynthesis does not take place until chlorophyll 

 has been formed. So in variegated leaves, photosynthesis does 

 not take place in the white portions because chlorophyll is absent, 

 but it does take place in the green parts of such leaves or in such 

 parts as have chlorophyll. Photosynthesis does not, therefore, 

 take place in the roots, not even in the roots of green plants, nor 

 in stems where chlorophyll is not present. Experiments with 

 chlorophyll-less plants like beech drops (Epiphegus), the Indian 

 pipe (Monotropa}, and the fungi and bacteria $ show that photo - 



* The symbol for starch is probably some multiple of this and is usually 

 written (C 6 H 10 O 5 )N. 



f There are some few exceptions. The first leaves of pine seedlings have 

 chlorophyll leaves even grown in the dark. 



t A few bacteria, however, are known to be able to form their own car- 

 bohydrates. The nitrite and nitrate bacteria which convert ammonia com- 

 pounds into nitrites and nitrates in the soil obtain energy from the chemical 

 process of making nitrites and nitrates, so that they can assimilate the CO 2 

 of the air. This is not photosynthesis however, since light does not supply 

 the energy. It is chemo synthesis. 



