B 



'W. 



Plate V. Effect of length of day on plants. A, scarlet sage (Salvia splendens) , 

 a short-day plant; B, lettuce, a long-day plant. The day lengths to which the plants 

 were subjected are indicated on the pots. (From Hill, Overholts and Popp's Botany, 

 McGraw-Hill Book Co., 1936.) 



