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 Me Bia, HO Renamer 
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 W@Fd through 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- 
