58 INTRODUCTION TO BOTANY 
of cork which form outside the green bark. Photosynthetic 
work is also done by the stems of most common annual plants 
of the farm and garden, such as corn, beans, peas, and potatoes. 
Fie. 89. Twigs of coffee tree, showing how leaves are supported so as to 
give them complete exposure to light 
57. The stem raises leaves into the light. Competition for 
light is extremely common among plants. One of the main 
reasons why the surface of the earth in a very dense forest 
—the forest floor, as it is called —is comparatively bare of 
flowering plants is that they cannot get enough light there 
to live. In a cornfield it often seems ax if the weeds were 
