FOOD MAKING 



81 



total product of photosynthesis is very great. It has been 

 expressed in a number of ways. It would appear as a stagger- 

 ing amount if it should appear as sugar in our trees or on our 

 lawns. Transeau has figured that an acre of corn makes 

 about 200 pounds of sugar per day and an acre of apple trees 

 about 93 pounds per day. Sugar cane and sugar beets pro- 

 duced thirty-two million tons of sugar in the 1930-1931 crop 

 season, to which must be added the sugar used to build their 

 plant bodies. Dr. Arthur has estimated that the human race 

 uses about 0.2 per cent of the product of all photosynthesis 

 as food, and all animals great and small use less than 2 per 

 cent. The other 98 per cent is destroyed by bacteria, other 

 fungi, and fire. 



The gardener must depend on a high photosynthetic rate 

 to be successful. He can improve many of the necessary con- 

 ditions but he has no power over many of the other governing 

 factors, such as temperature and sunlight. Many experi- 

 ments with the different colors of light indicate that plants 

 can use any one color successfully in photosynthesis, but that 

 the red and blue are slightly more effective. He can give the 

 plants enough space to come in direct sunlight by avoiding 

 overcrowding. He can make use of the season of the year 

 when the temperature is best. Some measurements have 

 been made which show photosynthesis may go on three times 

 as fast at ninety degrees as it does at sixty degrees tempera- 

 ture, while for other plants, as potatoes, seventy degrees F. 

 has been found to be optimum. In some cases the rate may 

 be doubled with an increase in temperature of ten degrees C. 

 The soil fertility may be improved. Nitrogen may be ap- 

 plied in excess at an early stage in order to grow larger leaves 

 to be exposed to the light; this is often spoken of as "giving 

 the plant a quick start." An optimum soil moisture content 

 will enable the stomata to remain open, admitting the maxi- 

 mum amount of carbon dioxide. This is accomplished with 

 greatest success in some of the irrigated regions, as indicated 



