330 JCSJSSONS WITH PLANTS 



manifested in the germinating bean? Do thg two 

 parts take these opposite directions even when the 

 beans germinate in a dark place ? We shall find 

 that there is an inherent, or inborn, tendency for 

 the root to grow down and the stem to grow up. 



405a. The discussion of the physiological causes which have 

 determined this differentiation between the root and stem is not 

 germane to this book ; although it may be said that gravitation 

 plays an important part in the movements. For the purpose of 

 designating some of these facts or phenomena, the words geotropism 

 and heliotropism have been used, — the former designating move- 

 ment into or towards the earth, and the latter movement towards 

 the light. 



Suggestions. — The pupil should make these tests with beans. 

 He will find other interesting points', if he watches the process of 

 germination closely. When some of the seeds have produced straight 

 roots an inch or so long, remove them carefully and hang them 

 with the root uppermost in a moist and warm atmosphere, as under 

 a bell-jar or inverted glass bowl which is set in water. Observe 

 how the roots tend to turn downwards and the plumule to turn 

 upwards. Or, sprouting seeds may be placed in a horizontal posi- 

 tion. It is interesting to observe how the root gets around stones 

 and other hard objects in the soil. The roots of any plant which 

 grows in very stony or hard, gravelly soil are good subjects for 

 observation. Radishes are also interesting for germinating studies; 

 and they show heliotropism quickly and emphatically when growing 

 where the light all comes from one direction, as from a side 

 window. 



The beans may be planted in pans or boxes which are set in 

 the windows of the school-room, although care should be taken 

 that the soil does not become too dry if it is exposed directly 

 to the sun. The handframes mentioned in Obs. Ixxiii. will be found 

 to be useful with which to make germination studies. The pupil 

 usually takes more interest in the experiments, however, if he has 

 them constantly under his eye. Perhaps each pupil can be pro- 



