Light in Greenhouse Culture 63 



Root Development Influenced by the Color of the 



Glass 



It has already been seen that different rays of the 

 solar spectrum may modify the parts of the plant 

 above ground. The same effects may also appear in 

 the root system of such plants. The root system is 

 considerably smaller in the red hothouse than it is in 

 the white hothouse. In the hothouse with green 

 glass, the root system is very poorly developed, 

 while in the blue there is almost no root system. 



Anatomy of the Plant as Influenced by Dif- 

 ferent Rays of Light 



As we have seen, different rays of light are capa- 

 ble of influencing the growth of plants. The same 

 is also true of the structure of plants. Flammarion 

 has found that sensitive plants, for instance, when 

 grown in a white hothouse, possess a thicker epider- 

 mis, more numerous wood fibers in the stem, and 

 the pith was much less developed than was the case 

 with similar plants grown in red, green or blue hot- 

 houses. 



Effect of White and Colored Light on Trans- 

 piration 



The effect of various lights on transpiration is 

 shown in Table lo. 



