152 



INDIVIDUALITY IN ORGANISMS 



of the stem, but physiological isolation of parts and 

 reproduction of new individuals afford the only means 

 of demonstrating experimentally the existence of domi- 

 nance and its varying range. From among the accu- 

 mulated data concerning what the botanists commonly 

 call correlation, a few simple, well-known experiments 

 are briefly described to 

 show how readily physio- 

 logical isolation and repro- 

 duction may be brought 

 about in plants. 



The young seedling of 

 a leguminous plant (pea, 

 bean) possesses the general 

 form indicated diagram- 

 matically in Fig. 84. The 

 further normal develop- 

 ment of the stem consists 

 primarily in its elongation 

 and the development of 

 leaves by the activity of 

 the growing tip at its 

 apical end, but if this 

 growing tip is removed a 

 new growing tip, or in some 

 cases more than one, arises 

 from the axillary region of each cotyledon, as indicated 

 in Fig. 85. These axillary shoots very rarely appear 

 when the original growing tip is present and active, but 

 their development results regularly from its removal. 

 If both of the shoots grow at about the same rate they 

 may both continue to develop and so give rise to two 



FIGS. 84, 85. Diagrammatic 

 outlines of leguminous seedlings, 

 illustrating effect of removal of 

 growing tip: Fig. 84, uninjured 

 seedling; Fig. 85, development of 

 shoots from axils of cotyledons 

 after removal of stem-tip. 



