PLANT FOOD AND PLANT GROWTH 31 



have power to attack and decompose other substance. Formic 

 aldehyde is often used as a disinfectant, and a 40 per cent solution, 

 known as " formalin," is employed (at the rate of one pound of 

 formalin in 50 gallons of water) to destroy smut in seed oats, for 

 example. 



A remarkable property of the aldehydes is the power of condensa- 

 tion, by which two or more molecules are condensed into one. 

 Thus, two molecules of formic aldehyde, or monose, 2 CH 2 O, may 

 become one molecule of diose, C 2 H 4 O 2 ; while three molecules may 

 form one of triose, C 3 H 6 O 3 ; and four may form tetrose, C 4 H 8 O 4 ; 

 and five, pentose, C 5 H 10 O 5 ; etc. 



The condensation process is so rapid that formic aldehyde itself 

 is found in plants only in very small amount, while the condensa- 

 tion products constitute commonly 80 to 90 per cent of the entire 

 plant. The ending -ose means sugar, and the prefix mon-, di-, tri-, 

 etc., designate the number of carbon atoms in the molecule. The 

 following may illustrate this series of carbohydrates: l 



CH 2 O, monose (formic aldehyde). 

 C 2 H 4 O 2 , diose (unknown). 

 C 3 H 6 O 3 , triose (glycerose). 

 C 4 H 8 O 4 , tetrose (erythrose). 

 C 5 H 10 O 5 , pentose (xylose). 

 C 6 H 12 O 6 , hexose (glucose). 

 -12^240 12 , lactose (milk sugar). 

 C^HjgOy, sucrose (common sugar). 



Here we may see the possible development of the well-known 

 glucose, milk sugar, and common sugar (obtained from sugar cane 

 and sugar beets), as condensation products from monose, or formic 

 aldehyde, formed in the living plant from carbon dioxid and water. 



1 It cannot be considered as absolutely proven that formic aldehyde is always 

 the first product of this fixation process; and, if it is, it seems that the first condensa- 

 tion product results from the union of three molecules, because the compound 

 that might be called diose is not found in plants and is not known to exist. 



The known facts are that carbon dioxid is condensed in the leaves of plants 

 and that oxygen is given off in the proportions required for this reaction (aside from 

 the oxygen normally exhaled), also that formic aldehyde is found in plant leaves, 

 that aldehydes have the power of condensation, and that multiples of the formic 

 aldehyde molecule are actually present in plants (as hexose) or represented (as 

 in starch, cellulose, pentosans, etc.). 



