THE SPERMAPHYTES. 



247 



FIG. 172. Seedling of Bean, 

 showing positive geotro- 

 pism. G is a bell jar 

 standing in an open dish, 

 B, which contains water; 

 S, the seedling. (After 

 Detmer.) 



placed in strong sunlight with favorable conditions of 

 heat. In two or three hours the radicle obeying geotro- 

 pism pushes the pan of the balance down. 



28. Study geotropism. Germinate Beans until the 

 radicles are half an inch long. Pin the Beans to large 

 corks, and insert the corks in 



bottles nearly full of water so 



that the radicles are placed hori- 

 zontally. Tip the bottles so as 



to wet the seedlings. Place in 



strong sunlight. After a time 



notice that the end of the radicle 



turns downward. It is positively 



geotropic. The plumule tends to 



turn upward. It is negatively 



geotropic. Continue the study 



of positive and negative geotropism, using young plants of 



Onions, Tulips, and Hyacinths, 

 fixing them in horizontal posi- 

 tions after the growth is well 

 started, and supplying suitable 

 conditions for nutriment, light, 

 and heat. Also sow Peas or 

 Beans in a hanging sponge ; 

 keep well watered. After the 



FIG. 173. -Young Onion plant, seedlings are well started, turn 



showing negative geotropism. the SDOllge Upside down and 

 (After Frank.) j ii~u xu j- 



study the changes in the direc- 

 tions of growth of the stems and roots. 



29. Study heliotropism. 



a. Grow seedlings of Canary Grass or Beans in a wet 

 sponge hanging in a box painted black on the inside. 

 The box should have a removable, light tight cover, and, 

 on the side toward a window, a hole which is closed with 

 a cork until the seedlings are well started. The cork is 



