100 



GENERAL BIOLOGY 



discontinuous. But the discontinuity is thus only 



apparent, not real. 

 Indeed there is always 

 retained, not only a 

 physiological, but also 

 a certain physical con- 

 tinuity between the 

 cells. 



INFLUENCE OF EXTER- 

 NAL CONDITIONS ON 

 GROWTH 



Light. One of the 

 factors of most signifi- 

 cance in the normal 

 growth of animals and 

 plants is that of light. 

 It makes a great differ- 

 ence, however, whether 

 this light is diffuse or 

 whether it is the direct 

 sunlight. Sunlight 

 completely inhibits the 

 growth of many Pro- 

 tista and lower plants 

 (bacteria, molds, etc.) 

 and destroys the organ- 

 isms. For this reason 

 sunlight is one of the 

 most effective sterilizing 



FIG. 35. Peas grown 6 days in 

 darkness (a), in about i light (6), and 

 open in greenhouse (c). (From Dug- 

 gar's Plant Physiology.) 



