APPENDIX 
PHOTOSYNTHESIS 
The chemistry of photosynthesis is not completely known, 
but some of the simpler aspects of it may prove valuable to 
the student. The chemist’s formula for water is H,O, in 
which H stands for hydrogen and O for oxygen, and the 
figure 2 indicates that two parts of hydrogen are united with 
one part of oxygen. Similarly, CO, indicates that one part 
of carbon is united with two parts of oxygen to form carbon 
dioxide. When these compounds are broken up, there is, for 
a very brief time at least, free C. H, and O. If one unit of 
each compound (H,O and CO,) is thus broken up, there 
will be two H, one O, one C’, and two O — or in all three O. 
After photosynthesis has been going on for some time, starch 
is usually formed. Starch consists of (C,H,,O,),. This 
means that six parts of carbon, ten parts of hydrogen, and five 
parts of oxygen unite to form starch, and the x means that 
the unit C,H,,O, does not appear singly, but that an unknown 
number of them are united. Disregarding the fact that several 
of the starch units are held together, and considering the single 
unit C,H,,O,, we may be able to see what happens in the work 
of photosynthesis. To secure the amount of carbon necessary 
to form starch, six times the unit CO, must be taken, since 
six units of carbon are to be used. To secure the needed 
amount of hydrogen, five times the unit H,O must be used, 
since there must be ten units of hydrogen, and two are secured 
with each unit of water. We have therefore 6 (CO,) and 
5(H,O). When the energy of the sun has broken these 
things into their constituent parts, there are 6(C), 12 (O), 
10 (H), and 5 (O)—or 17 (O) in all. But starch consists of 
343 
