198 THE TEACHING BOTANIST 



VII. Plasticity of the Shoot and Root in Form 



and Size 



28. In the Bean, Coleus, and Balsam you have studied 

 three fairly typical Mesophytes. The most 

 typical or average form would show a vertical, 

 independent, cylindrical stem, growing by vegeta- 

 tive points at its tip and in the axils of the leaves, 

 and continued into a main root at its lower end. 

 The leaves would stand in definite positions 

 (producing the nodes), separated by spaces (the 

 internodes), and would be arranged either in 

 whorls of two or more at a node, or with but 

 one at a node, and forming a spiral. The leaves 

 would be simple, thin, horizontal, toothed, ovate 

 in form, with a petiole and two stipules. But 

 such a condition is an ideal one and not realized 

 in any single plant, and very wide deviations 

 from it occur in plants as result of adaptation 

 to special habits. 



In what respects are the plants on the tables modi- 

 fied from the typical or average condition, and 

 what is the probable ecological meaning of the 

 modification ? 



Your record, of eight plants, should bring out 

 the name of the plant and scale of the draw- 

 ing. It is not necessary always to draw the 

 entire plant, but only its peculiar features. 



