O SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 94 



the enclosed controls, the number and weight of grain were greater 

 for the carbon-dioxide-treated cultures. 



The weight per grain was somewhat higher for the plants receiving 

 the greater quantity of carbon dioxide. One other point of interest 

 is that these same plants put out a greater number of tillers than the 

 ones treated with less carbon dioxide. Those in no. 6 appear to be 

 an exception. 



PLOT EXPERIMENTS 



Owing to the poor stand in one of the 2 x 2- foot plots from the 

 planting made on April 14, these three plots were replanted on May 9. 

 Because of this delay, seeds sprouted in the laboratory were used for 

 the second planting. A good stand was obtained by May 14, at which 

 time the carbon dioxide-air mixture at the approximate rate of 2 

 liters a minute was turned into the glass enclosure surrounding plot 

 A; B served as the enclosed control plot, and C as the open one. On 

 May 17 the glass sides were increased in height from 30 to 60 inches. 



The results of this experiment are summarized in table 3. The 

 general appearance and arrangement of these three plots and of the 

 6-pot experiment described above are shown in plate 4. The wheat in 

 the three plots, harvested July 25, is illustrated in plate 5. The dry 

 weight data were determined after the plants were air dried for about 

 2 months. 



Table 3. — Suimiiary of 1934 Experimcnl imth Wheat Grozvn in 3 x 2-foot Plots 



Plot A Plot B 



(in glass (in glass Plot C 



Data enclosure) enclosure) (open) 



.Average CO2 concentration (relative to 



normal air) 3.8 i.i 0.9 



Number of seeds planted 36 36 36 



Number of plants harvested 34 33 31 



Average data per plant: 



Weight (grams) at harvest i4-52 6.39 3.47 



Weight after air drying 8.02 5.00 3.02 



Weight of water lost in drying... 6.50 1.39 0.45 



Number of heads 7.44 4.03 2.74 



Weight of heads 2.88 2.51 1.26 



Weight per head 0.39 0.62 0.46 



Weight of straw 5.14 2.49 1.75 



Weight of grain 0.85 1.70 0.77 



Number of grains 26.08 57-70 37-52 



Weight per grain 0.0326 0.0295 0.0205 



Number of grains per head 3.51 14-32 13-68 



At time of harvest the total weight per plant of those treated with 

 carbon dioxide was over twice that of the enclosed control plot (B) 

 and over four times that of the open control plot (C). This great dif- 

 ference was due largely to the water content as is evidenced by the 

 dry weights, which, however, still indicate a substantial increase of 



