June 10, 1918 Transpiration of Corn and the Sorghums 603 



transpiration per unit of leaf surface was practically the same as that of 



the sorghums. At the later stages of growth, however, when the plants 



had attained their full leaf development, the rate of transpiration per 



unit of leaf surface was often twice as high for the sorghums as for the 



corn plant under the same conditions. The differences between the rate 



of transpiration of the corn and sorghum plants is more marked when the 



plants are under severe climatic conditions than when they are under 



more favorable environments. This was noted in the differences between 



the transpiration rate per unit of leaf surface of these plants during the 



earlier and later periods of the day as compared to those periods of the 



day when the evaporating power of the air was high. 



The results of these experiments with corn and the sorghums seem to 



indicate that in most cases a small leaf surface is the most important 



factor in reducing the loss of water from these plants. The corn, with 



its large extent of leaf surface as compared to the sorghums, always 



transpires more water per plant in a given period than the sorghums. 



It is not able, however, to absorb water from the soil and to transport 



it to so large a leaf surface in sufficient amount to satisfy the evaporating 



power of the air. As a result of this deficiency, the rate of transpiration 



per unit of leaf surface is lower than it would be if water were supplied 



in sufffcient quantity to meet the demands of the evaporating power of 



the air. The sorghums, on the other hand, have, as compared to the 



com, a much smaller leaf surface and always transpire less water per 



plant during any given period than the corn. Since the sorghums have 



such a small leaf surface exposed for the evaporation of water and since 



they have a more elaborate root system than the corn, they are able to 



absorb water from the soil and transport it to the leaves in sufficient 



amount to satisfy the evaporating power of the air. As a result of this, 



their rate of transpiration per unit of leaf surface is higher than that of 



the corn plant. 



SUMMARY 



Five experiments were conducted in 191 6 and eight in 191 7 to deter- 

 mine the relative transpiration of corn and the sorghums. Pride of 

 Saline corn, Blackhull kafir, Dwarf Blackhull kafir, and Dwarf milo were 

 used in 1916; and in 1917, in addition to these, Freed's White Dent com, 

 Sherrod's White Dent corn, Freed's sorgo. Red Amber sorgo, and feterita 

 were used. The plants were grown in large galvanized-iron cans with a 

 capacity of about 120 kilos of soil. The soil used in 1916 had a water 

 content of 18 per cent and a wilting coefficient of i i.i , while the moisture 

 content of the soil used in 191 7 was 22 per cent and had a wilting coeffi- 

 cient of 1 5. 1 . The moisture content of the soil was kept as nearly constant 

 as possible by the addition of water to the cans from three to four times 

 each day during the time of the experiments. The number of plants 

 grown in each can was reduced to one plant for eac;h of the varieties of 



