72 



EXPERIMENTS WITH PLANTS 



often lifting up a good -sized lump of earth on emerg- 

 ing; the Castor-bean doubles and twists (Fig. 58), like 

 an athlete straining every muscle ; why does it have so 

 much trouble? Does the growth of the seed-leaves 

 while still underground account for it ? Suppose we re- 

 move all hindrances from the Castor-bean; will the 

 stem still form the characteristic "loop"? Allow some 

 to germinate on the surface of the soil, or, better, in a 



flower -saucer which has been 

 boiled (since Castor -beans are 

 very apt to mould). Cover 

 this with a piece of glass which 

 has been boiled in water or 

 rinsed in two per cent forma- 

 lin. Remove the coats from 

 a part of the seeds, so that 

 they may be freed from all 

 hindrances which might cause 

 the formation of the "loop." 

 Place some with the caulicle 

 downward, others with the caulicle upward. Try the 

 same experiment with other seeds which form a "loop." 

 What part of the plant forms the "loop" in the Onion ? 

 What plants do not form a "loop" ? (Notice especially 

 Corn and Grasses.) 



How much opposition can the stem overcome in forc- 

 ing its way upward? We may test this by means of 

 the apparatus shown in Fig. 59. Find two bottles 



58. Castor- bean twist- 

 ing itself into a loop 

 in its efforts to pull 

 the seed-leaves out 

 of the ground. 



