PHYSIOLOGICALLY ACTIVE GASES 



149 



from a multiplication of cells (hyperplasia) and from an increase in size of 

 some of the cells (hypertrophy). Fig. 56 shows the effect of ethylene in 

 inducing proliferation of tissue in the lenticels of young Hibiscus stems. In 



Figure 56. Twigs of Hibiscus cut from tree in lat« January and placed in moist 

 chambers for 10 days. Left: control in air. Right: treated in ethylene 10 ppm. Note 

 that ethylene induced undifferentiated outgrowth from the lenticels and stopped bud 

 growth. 



the picture the outgrowths look like roots. Instead they are undiiTeren- 

 tiated tissue. It will be noted also that ethylene hindered the grou-th of 

 buds. The enlargement in the tip of the sweet pea seedling (Fig. 51) in- 

 duced by ethylene probably results mainly from cell enlargement. 



When the illuminating gas flowed through the soil more rapidly, this 

 response did not occur, but the roots and base of the stem were killed. As 



