56 FOUNDATIONS OF BOTANY 
and, if so, at what temperature the wilting begins. Finally, remove 
the tube from the ice and place it in warm water (about 80°). 
Observe the effect and note the temperature at which the plant, 
if wilted, begins to revive. Find an average between the wilting 
temperature and the reviving temperature. For what does this 
average stand? . f 
68. Movements of Young Roots. — The fact that roots 
usually grow downward is so familiar that we do not 
generally think of it as a thing that needs discussion or 
explanation. Since they are pretty flexible, it may seem 
as though young and slender roots merely hung down 
by their own weight, like so many bits of wet cotton 
twine. But a very little experimenting will answer the 
question whether this is really the case. 
EXPERIMENT XVIII 
Do all Parts of the Root of the Windsor Bean Seedling bend down- 
ward alike ?— Fasten some sprouting Windsor beans with roots 
about an inch in length to the edges of a disk of pine wood or 
other soft wood in a soup-plate nearly full of water and cover them 
with a low bell-jar. Pins run through the cotyledons, as in Fig. 26, 
will hold the beans in place. When the roots have begun to point 
downward strongly, turn most of the beans upside down and pin 
them in the reversed position. If you choose, after a few days 
reverse them again. Make sketches of the various forms that the 
roots assume and discuss these. 
EXPERIMENT XIX 
Does the Windsor Bean Root-Tip press downward with a Force 
_ greater than its Own Weight ?— Arrange a sprouted bean as shown 
in Fig. 26, selecting one that has a root about twice as long as the 
diameter of the bean and that has grown out horizontally, having 
been sprouted on a sheet of wet blotting paper. The bean is pinned 
