NO. 15 AERIAL FERTILIZATION OF WHEAT JOHNSTON 3 



As can be seen from the table, the plants that received both addi- 

 tional light and carbon dioxide were heavier and contained a greater 

 quantity of carbohydrates than the control plants. No signs of heading 

 in the control plants were noted at time of sampling, whereas those 

 in greenhouses i and 2 had been in head for some time. These authors 

 conclude that : 



Small grains, such as barley and spring wheat, in contrast to potatoes, will 

 grow and yield well at a high temperature (78° F.) if given additional light and 

 carbon dioxide. The production of these grains is not favored by low temperature 

 when day length is long and carbon dioxide supply is abundant. The weight per 

 plant of barley increases with day length up to a 19-hour day. Total carbo- 

 hydrates also increase and nitrogen decreases. The feeding of nitrate was found 

 to make little or no difference in the total percentage of nitrogen in the barley 

 plant, the percentage remaining high only when carbohydrate synthesis was 

 restricted by short days. 



EXPERIMENTATION 



In the laboratory experiments of Hoover, Johnston, and Brackett, 

 in which growth was entirely under artificial conditions, the wheat 

 plants were confined to a double-walled glass cylinder with their roots 

 extended into a flask of nutrient solution. In the first type of experi- 

 ments run outside, Marquis wheat was planted in six 8-inch earthen- 

 ware pots (not glazed) containing a good garden soil. The pots were 

 buried to their rims in wet peat moss placed in a long, narrow cypress 

 box. Cylinders 30 inches in length with conical tops were made from 

 clear cellulose acetate sheeting and so constructed that they fitted into 

 the tops of the pots. The purpose of these cylinders was to confine 

 air of a given carbon-dioxide concentration about the plants. In order 

 to insure a fairly constant carbon-dioxide concentration, the desired 

 air mixture was introduced through a glass tube emerging centrally 

 just above the surface of the soil. Holes cut in the cylinders at the 

 tops just beneath the aprons of the cones provided an exit for the 

 air. 



It was thought the flow of air through these cylinders would be 

 sufficient to keep the plants cool. It was soon realized, however, that 

 additional cooling would have to be employed. A means was devised 

 for flowing a thin sheet of water over the outer surfaces of the 

 cylinders. Near the tops of the cylinders small jets of water from 

 copper tubings wet short cloth curtains wrapped around the upper 

 portions of the cylinders. This gave a fairly even distribution of 

 water over the surfaces of the cylinders. Even with this additional 

 equipment, the temperatures within the cylinders were still excessively 

 high on clear days. This was in part due to the high temperature of 

 the tap water used for cooling, which frequently had a temperature of 



