LETTER V 



Crocuses Effect of Light on Plants Actinism Yellow Flowers 

 and Blue Flowers Crocuses caught by Snow Leaves ab- 

 sorbing Heat. 



27 f A March 1886. 



DEAR MARCO 1 intended to have added 

 something about crocuses to my last letter, 

 but thought it long enough as it was. Per- 

 haps you may have noticed that though the 

 yellow and orange crocuses have far the 

 largest bulbs, the blue, lilac, and white ones 

 exceed them in the size of their flowers. Is 

 it possible that this is due to the effect light 

 has on them ? Photographers tell us, or did 

 so years ago, that the sun's rays possess 

 another power besides light and heat, which 

 they call actinism ; it is this power which 

 affects the salts of silver and turns them dark 

 more than the light itself. This actinism is 



