138 



THE INDIVIDUAL ORGANISM 



complex coordinative mechanisms, and digestive apparatus, all of which 

 are largely without counterparts among plants. 



The requirements of the green plant are fundamentally different. Typi- 

 cally, it must have an extensive absorptive (root) surface for taking in 

 water and dissolved inorganic substances. It must also have a large 

 chlorophyll-bearing (leaf) surface exposed to light for the capture of 

 energy for photosynthesis, and to air (or water), for obtaining the neces- 



Reproduction 



Flower 



Leaf 



Stem 



Root 



Fig. 9.2. Diagram of the important structures and functions of a seed plant. (Modified from 

 Turtox chart, courtesy General Biological Supply House, Inc.) 



sary carbon dioxide. The relatively great expanse of surface that these 

 requirements necessitate simplifies the problem of respiration and elimi- 

 nates need for an elaborate breathing mechanism but introduces other 

 problems in the use and control of evaporation of water. Since the light, 

 water, carbon dioxide, and minerals that the plant requires are almost 

 everywhere available, locomotion is nonessential and is largely precluded 

 by the necessity of a root system. Unable to escape their enemies by 

 flight or active resistance, plants avoid or minimize damage by rapid 

 repair of injury and by such protective adaptations as armoring bark, 

 defensive spines, or repelling taste. Rigidity and strength are called for 



