10 LUTHER BURBANK 



If you closely examine the calla you will 

 observe that what you would casually speak 

 of as a single blossom is in reality a case or 

 shield in point of fact a modified leaf- 

 twisted into a sort of cornucopia and adjusted 

 about a central stalk or "spadix" on which 

 many minute arid inconspicuous blossoms are 

 clustered. 



The object of this arrangement is doubtless 

 in part to give protection to the flowers, but 

 largely to supply a conspicuous signal to attract 

 night-roving insects, in particular various species 

 of small gnats and flies, 



In point of fact the white canopy of the calla 

 affords a very convenient place of refuge for 

 numerous small insects. 



Tests have shown that the air inside the calla 

 "blossom," particularly toward its base, where 

 the insects congregate, is perceptibly warmer 

 than the outside air. 



It has been proved by recent experiments 

 that the chemical processes associated with plant 

 growth generate heat. Germinating seeds, for 

 example, give out a measurable quantity of heat. 

 So it is not strange, perhaps, that the partially 

 confined air at the base of the tubular calla 

 flower case is at all times a little warmer than 

 the surrounding atmosphere. 



