HELIOTROPES, OR SUNFLOWERS. 181 



peduncles increase much in length, and slowly curve 

 downwards, but the short, upper, hooked part, 

 straightens itself. Ultimately, the pods reach the 

 ground, and if this is covered with moss or dead 

 leaves, they bury themselves. We have often seen 

 saucer-like depressions formed by the pods in damp 

 sand or sawdust, and one pod (three-tenths of an 

 inch in length) buried itself in sawdust for three- 

 quarters of its length. The peduncles can change 

 the direction of their curvature, for if a pot with 

 plants having their peduncles already bowed down- 

 wards, be placed horizontally, they slowly bend at 

 right angles to their former direction towards the 

 centre of the earth. We, therefore, at first, attributed 

 the movement to geotropism (turning towards the 

 earth), but a pot which had lain horizontally with 

 the pods all pointing to the ground, was reversed, 

 being still kept horizontal, so that the pods now 

 pointed directly upwards ; it was then placed in a 

 dark cupboard, but the pods still pointed upwards 

 after four days and nights. The pot, in the same 

 position, was next brought back to the light, and 

 after two days there was some bending downwards 

 of the peduncles, and on the fourth day two of them 

 pointed to the centre of the earth, as did the others 

 after an additional day or two. Another plant, in 

 a pod which had always stood upright, was left in 

 the dark cupboard for six days ; it bore three pe- 



