HOW PLANTS ARE INFLUENCED . 347 



weak. The leaves 1 (in most plants) remain small and 

 pale in color. Hairs and even prickles tend to dis- 

 appear in darkness. 



It is well known that intense light causes a greater 

 intensity of coloring of fruits, flowers and other colored 

 parts of plants: this is especially noticeable in moun- 

 tain regions. Compare the colors of flowers in shady 

 woods with those in the sunlight of open meadows. 



Light also affects the abundance of flowers and 

 fruit. Many plants bloom little or not at all in poor 

 light, while in strong light they do so abundantly. 

 This is noticeable in house -plants cultivated at a north 

 or northeast window, as compared with those grown at 

 a south window. Tfye effect is due partly to the fact 

 that with better light the leaves produce more food for 

 the nourishment of the flowers and fruit, partly to the 

 direct action of the light (and temperature) on the 

 organs themselves. If possible, make experiments on 

 this point. Some plants can be kept for years in 

 healthy vegetative condition at an intensity of illumi- 

 nation which is too low to permit them to blossom. 

 Observe plants that are partially shaded (as by a house 

 or hedge) , and note especially whether more blossoms 

 are formed (blossoms formed on one side may, by 

 twisting, appear on the other) on the side which is 

 shaded or on the side which is exposed to the light. 



1 In many Monocotyledons the leaves continue to grow in darkness. The 

 scale-leaves of subterranean stems often develop into green forage-leaves if 

 exposed to light (e. g., Hawkweeds). 



