TEMPERATURE AND LIGHT 



231 



It is very generally recognized that many plants grow most 

 rapidly during the night ; this is partly due to the retarding 

 action of the sun's rays and partly due to the greater humidity 

 of the atmosphere, but the growth is always with the food that 



FIG. 106. Ivy leaves on a wall showing the arrangement with very little overlapping. 



was manufactured during the day. It is also well known that 

 sunlight will kill many species of bacteria. 



Relation of Plant to Sunlight. It is well known that plants 

 growing in a window develop so as to bring the leaves into the 

 proper light relationship. Also that potatoes which germinate in 

 darkened cellars produce long shoots which grow in the direction 

 of the liffht (see paare 218) . Plants in the open are subject to the 



