66 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? 



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 XVm 



Do all Parts of the Eoot 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 beU-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 



