Lecture 3, July 7. 



The influence of liglit on vegetation is one of the most 

 important factors in plaxit life. Light is absolutely necessary 

 to all green plants, indirectly to all life. If things are 

 parasites or saprophytes, they are indireetly dependent. 



Chlorophyll depends on light. Plants kept in the dark do 

 not develop it and even lose what they had, as in the bleachin,:: of 

 celery. 



Growth independent of sunlight is the result of stored-up 

 food. A potato will grow in a dark cellar. Fungi have "been 

 found growing in caves on hits of tallow, droppings from the rainers ' 

 candles. Plant growth is influenced not only hy intensity "but 

 also by duration of light. Oats will ripen more quickly in some 

 northern sections than in those lying further south. The reason 

 for this is supposed to be partly the continued periods of light 

 in the northern regions.. 



Other colors, especially in autiimn, are associated with sunlight. 

 This coloring is usually found on the upper side of the leaf or 

 on the under side if that has been exposed to the direct sunlight. 



The opening and closing of flowers is also influenced by the 

 light. Other factors also help to produce this effect. Too much 

 light injures the chlorophyll. 



Plant forms are greatly influenced by the intensity and duration 



