Chap. 4 PLANTS PROVIDE FOR THEMSELVES AND THE ANIMALS 59 



istic of its species and of itself — the barrel cactus of the southwestern desert, 

 the American elm, the jack-in-the-pulpit. There is a strict division of labor in 

 the plan of the body; different parts perform particular functions such as 

 protection, support, and water transport (Fig. 4.7). The plant body has two 

 main regions, the shoot system of stem and leaves which is intimate with the 

 atmosphere and the root system which is correspondingly intimate with the 



soil. 



Stem. The stem or axis is a support and a highway. Its first function is the 

 raising of leaves to the light, of flowers upward for light and pollination, of 

 seeds in position for better dispersal. Its second function is the distribution of 

 water and nutrient solutions and gases throughout the plant. In most plants, 

 the stem is a cylinder that tapers at the top and gives off branches that are 



Absorption 



Water 

 Salts-- 



Oxygen 



^^ >Respiration 



Fig. 4.7. A diagram indicating the main structures and functions of a seed plant, 

 the bean. The first leaves (cotyledons or seed leaves) are richly stored with protein 

 and contribute only slightly to photosynthesis. (Courtesy, Woodruff and Baitsell: 

 Foundations of Biology, ed. 7. New York, The Macmillan Co., 1951.) 



