of light. Trees of some sijecles ■will have different shapes when 

 standing alone or in forests. 



Many plants may he divided Into heliophilous (sTin-loving^ and 

 heliophohoixs (shade-loving) as most forest trees. If we arrange 

 forest trees according to their need of light, we would prohably 

 have an arrangement like the following :- 



larch, hirch, aspen, pine, linden, oak, beech. If a beech-nut 

 jean sprout in a beech forest while an oak cannot, tho final stage 



of our forests will be beech forests. 



All plants do not come under these divisions. Poison ivy 

 has a wide range. A plant which adapts itself to a large habitat 

 is plastic in its habits, 



Heat. 



Heat is one of the most important ecological factors, more 

 importetnt than light because of the great differences of heat 

 distribution on the earth's surface. All plants have a certain 

 heat range, from a maximum to minimum temperature. Neither of 

 these is best adapted to the life-work of the plants. They develop 

 best in temperature between called the optimum. This varies for 

 different plants and for different functions in the same plants. 



Heat influences chlorophyll-building, assimilation, respiration, 



transpiration, roof-activity, development of leaves and blossoms, 



growth, and movement. Variations below the minimum or above the 

 maximum are not necessarily fatal to plants, most of which can 

 endure a greater variation below than above. 



