THE DIFFERENTIATED PLANT 195 



ogy he should note that flowers (and fruits) originate where 

 buds do ; that new parts come either from terminal or axillary 

 buds and that buds produce stems bearing leaves as lateral out- 

 growths. If allowed to follow his own observations to their 

 conclusions, and not forced into seeing what is not there, he 

 will find that the plant, so far from consisting of a series of joints 

 (phytomera) springing one out of another, grows from contin- 

 ually advancing buds which put out the leaves laterally and 

 branch in the axils of these. The teacher will do well to 

 introduce here an illustrated account of the mode of origin 

 of leaves from vegetative points. The appearance of nodes 

 and internodes is thus not of primary importance, but is 

 incidental; properly, leaves do not stand at nodes; nodes are 

 places where leaves stand. The student can make out also 

 that the stem must grow through a considerable part of its 

 length, but most actively near its tip, and that leaves grow 

 all through their structure. He should also recognize that 

 the root is a single profusely branching structure, originating 

 from a stem. The ecology of leaf, stem, root, should, of 

 course, be fully explained. This exercise affords also a very 

 good introduction to phyllotaxy. 



The geotropism of the Coleus shoot may be diagrammed in 

 simple outline figures. 



The nodules on the roots of Beans, and their part in sup- 

 plying additional nitrogen to the plant, should be explained ; it 

 is a most interesting and important topic, fully treated in the 

 newer books. 



Most important are the facts shown by Experiment 3. It 

 proves the absorption of oxygen and elimination of carbon 

 dioxide by plants in growth, a process identical with that occur- 

 ring in animals ; and it should be the more clearly emphasized 

 here, since there is a general misunderstanding of the process, 



