Growth. 37 



shoot. What effect does this have on the buds and branches 

 below? Several days will be necessary to secure the full exhibi- 

 tion of the reaction. 



This experiment may also be repeated with young plants 

 of the tomato or any member of the squash family [Cuctirdi- 

 tacea). It may be seen as a result of the above tests that an 

 injury of one organ may be followed by the development or 

 more rapid growth of another one, some distance away, which 

 takes up the functions of the missing or damaged member. 

 AU parts of the body are most intimately connected, and 

 operate together ; when one is destroyed, impulses are trans- 

 mitted to all the others, which make the necessary adjust- 

 ment to carry on the work of the organism in the absence of 

 the missing member. 



30. Formation of new tissues in healing wounds. 

 ■ — Cut off some branches of a rapidly growing young tree, at 

 the beginning of the spring season, and follow the course of 

 the healing over of the surfaces of the wounded member. Make 

 sections of the tissues formed, and compare with those of the 

 stem formed in the customary manner. If time does not per- 

 mit, or if the season in which the work is performed is not 

 suitable to make the above experiment, find old cuts or inci- 

 sions on trees, and note the mass of tissue formed about wounds. 

 Compare structure with that of normal uninjured stems. If 

 the course of a healing wound is followed, it will be found that 

 a specialized mass of cells is formed over the cut surfaces, 

 which is afterward differentiated into wood, cork, and bark, 

 effectually closing the wound and protecting the injured part. 



Repeat the above tests with soft-bodied herbaceous species. 

 In some instances it will be found that the outer cells nearest 

 the injured surfaces merely dry up and form a corky layer 

 which prevents bleeding and bars the entrance of destructive 

 fungi and other organisms. (See " Practical Plant Physiology," 

 pp. 36-38.) 



