70 



STRUCTURE OF HIGHER PLANTS 



The fibrovascular bundles are made up of different types of woody cells, some pitted, others 

 ribbed and still others strengthened by spiral or circular thickenings on the walls. 



and pitted ducts until it reaches the chorophyll-bearing or green 

 cells, particularly those in the middle part of the leaf. The green 

 cells absorb the water from the tracheids. Here, again, absorp- 

 tion is a cell function. Oxygen for respiration and carbon diox- 

 ide for photosynthesis diffuse through the stomata in the lower 

 epidermis of the leaves, through the air spaces in the middle layer 



of the leaf, and, by means of 

 osmosis, pass into the green 

 cells. In these green cells, 

 photosynthesis, fat manufac- 

 ture, and protein manufacture 

 take place. These processes 

 are considered leaf functions 

 because they take place in 

 the green cells of the leaves. 

 Again the function of the 

 organism is really a cell func- 

 tion. 



When greatly magnified, a woody bundle of the ExCCSS food paSSCS into the 



corn stem shows many of the tubes which are the . . 



passageways for the food of the plant. SlCVC tubes and IS COnVCVed 



