GERMINATION AND GROWTH 49 



for six or eight days, and sketch it at successive intervals. After the stem 

 has directed itself well upward, invert the pot again, and watch the growth. 

 After a week remove the plant and notice the direction of the root. Sketch 

 it entire, showing the changes in direction of growth. 



At the same time that this experiment is arranged, lay another pot with a 

 rapidly growing plant on one side, and every forty-eight hours reverse the 

 position of the pot, laying it on the opposite side. At the end of ten or 

 twelve days remove the plant and examine. How has the growth of root 

 and stem been affected? 



What do we learn from these experiments and from Exp. 35 as to the 

 normal direction of growth in these two organs respectively? Can you 

 think of any natural force that might influence this direction ? 



EXPERIMENT 38. To SHOW THAT PLANTS WILL EXERT FORCE RATHER 

 THAN CHANGE THEIR DIRECTION OF GROWTH. Pin a sprouted bean to a 

 cork and fasten the cork to the side of a flat dish, 

 as shown in Fig. 69. Cover the bottom of the dish 

 with mercury at least half an inch deep, and over 

 the mercury pour a layer of water. Cover the 



whole with a pane of glass to keep the moisture in, 



,_, FIG. 69. Experiment 



and leave for several days. The root will force its showing the root of a seed- 

 way downward into the mercury, although the ling forcing its way down- 

 latter is fourteen times heavier than an equal ward throu s h mercury, 

 bulk of the bean root substance, and the root must thus overcome a 

 resistance equal to at least fourteen times its own weight. 



48. What growth is. With the seedling begins the 

 growth of the plant. Most people understand by this 

 word mere increase in size ; but growth is something more 

 than this. It involves a change of form, usually, but not 

 necessarily, accompanied by increase in bulk. Mere me- 

 chanical change is not growth, as when we bend or stretch 

 an organ by force, though if it can be kept in the altered 

 position till such position becomes permanent, or as we say 

 in common speech, " till it grows that way," the change 

 may become growth. To constitute true growth, the change 

 of form must be permanent, and brought about, or main- 

 tained, by forces within the plant itself. 



49. Conditions of growth. - - The internal conditions de- 

 pend upon the organization of the plant. The essential 

 external conditions are the same as those required for germi- 



