Light Filters 



The development of a series of glass screens suitable for 

 absorbing or transmitting various parts of the spectrum, 

 which ma}^ be useful in plant phj^siology, has now been 

 carried to such stage by Dr. D. T. MacDougal that we 

 are able to supply squares (6| x 6| in.) and bell jars 

 suitable for the ordinary experiments in growth, photo- 

 tropism and photosynthesis. 



The bell-jars are 14 inches in diameter at base, which is 

 roughly ground, 14 inches in height, the conical top 

 having a perforation suitable for cork, rubber stopper, 

 or special ventilating cap. 



Now Ready 



Red — A good monochrome transmitting to .610 u. 

 bell-jars only. 



Blue — Transmits blue and wave-lengths shorter 

 than .510 u. Sheets only. 



Orange — High transmission in red, and green, to 

 .530 u. Bridges the spectrum from red 

 to blue. Bell-jars. 



Terms on application 



The Plant World Tucson, Arizona 



