344 MASS. EXPERIMENT STATION BULLETIN 260 



period would be during the longest daylight exposures of the year. A 

 preliminary pot experiment indicated that a marked increase in bloom 

 could be obtained by supplementing the daylight of late fall and early 

 winter employing 100-watt electric light bulbs. 



An experiment based on this light factor in which four plots were 

 used was set up in January, 1929. Black curtains separated the plots 

 receiving artificial light from those receiving no artificial light at night. 

 In each plot 195 corms were planted and a careful record was made of 

 the number of flowering spikes and the number of flowers on each spike. 

 The results showed that light had caused an increase of 63 per cent in 

 the number of spikes and an average increase of 30 per cent in the num- 

 ber of flowers on a spike. 



The time of year has considerable influence on the time interval from 

 planting to flowering, and this time interval is increased by the use of 

 artificial light. In these experiments artificial light retarded the date of 

 flowering by approximately fifteen days. 



The variety Crimson Glow was used in conducting this investigation. 



Influence of Light Quality on Plant Growth. (A. V. Osmun). Prelim- 

 inary experiments have been conducted to test the effect of so-called 

 health glass (glass which transmits a considerable percentage of the 

 ultra-violet rays) on plant growth and development. Plantings were 

 made in a lean-to greenhouse in which one-half of the ordinary glass had 

 been replaced by Vita glass. Radishes grown under Vita glass showed 

 a gain of 71 per cent in weight of the entire plant and 124 per cent in 

 weight of roots as compared with an equal number of -plants grown under 

 ordinary glass. Similarly, lettuce gained 76 per cent in weight and 

 formed! much more compact heads when grown under Vita glass. No 

 consistent results were obtained with calendulas and pansies. 



The Effect of Pot Structure on Soil Temperature. (L. H. Jones). A 

 series of tests conducted with various types of plant containers has shown 

 that the structure of the container has a marked influence on the tempera- 

 ture of the soil. The regulation three-inch standard clay pot will main- 

 tain a soil temperature as much as 20° F. below that of the air in a 

 greenhouse on a hot day. On the other hand, a pot of vitreous material 

 or a glass tumbler will maintain a soil temperature that lags only 1° or 

 2" behind the rise and fall of the air temperature. 



Between these two extreme types of pots, the former very porous 

 and the latter with no porosity, there are intermediate types of pots 

 that maintain their soil temperatures according to the amount of moist 

 area presented by the pot to the air in the case of the porous pots, or 

 else the soil temperature will be influenced by the insulating value of the 

 pot material in the case of the non-porous pots. 



The cooling effect by evaporation of moisture from the outside of the 

 pot persists as long as the ]iot is able to withdraw moisture from the 

 soil) to moisten its surface. 



