58 



4- Plants grown in a series of colored glass houses in which 

 increasing amounts of ultra violet and blue regions of sunlight 

 were screened out. 



A series of slides showing the equipment and some of the 

 results on the general growth habit and flowering of the plants 

 was included. 



From the data presented the following conclusions were 

 drawn : 



1. Plants can be grown under artificial light using the gas- 

 filled incandescent type of lamp as a source. Many plants are 

 injured by continuous 24 hour exposure to artificial light. The 

 tomato is a good example of the maximum injury of this sort. 



2. A combination of 12 hours natural daylight and 6 hours 

 artificial light with additional carbon dioxide gas will produce 

 apparently normal plants. Eighteen hours of continuous arti- 

 ficial light produces much more injury. 



3. The time and amount of flowering is controlled in some 

 plants by the length of day, using either artificial or natural 

 daylight as a source as was first pointed out by Garner and 

 Allard of the U. S. D. A. Long day plants are attuned to flower 

 on the long days of summer while short day plants flower on 

 the short days of spring or fall. Flowering in other plants is 

 not greatly affected by the length of day. These are the so-called 

 "ever blooming" plants. These considerations apply to both 

 natural daylight and artificial light. The salvia was shown as 

 an example of a short day plant; lettuce and radish as long day 

 plants, and buckwheat as an "ever blooming" type. 



4. Plants show very little difference in growth habit or time 

 and amount of flowering whether they receive the ultra violet 

 of sunlight or whether this region is cut off down to 390 millimi- 

 crons. Certain colors are developed to a greater degree with 

 ultra violet light. When the blue region is screened out of 

 sunlight the plants grow in general much taller, show a lower 

 dry weight and less flowering and fruiting. The blue is appar- 

 ently necessary for producing both the normal form of plants 

 and in photosynthesis. 



Arthur H. Graves, 



Secretarv. 



