108 BOTANY. 



moisture, bending towards that side which is most moist, 

 and thus in a dry soil the roots are constantly guided into 

 those parts where the moisture is most favorable. 



185. Not only is the root-tip endowed with the power 

 of circumnutation, but, in the words of Mr. Darwin, "All 

 the parts or organs in every plant whilst they continue to 

 grow are continually circumnutating. If we look, for in- 

 stance, at a great acacia-tree, we may feel assured that 

 every one of the innumerable growing shoots is constantly 

 describing small ellipses, as is each petiole, sub-petiole, 

 and leaflet. The flower-peduncles are likewise continually 

 circumnutating; and if we could look beneath the ground 

 and our eyes had the power of a microscope, we should see 

 the tip of each rootlet endeavoring to sweep small ellipses 

 or circles, as far as the pressure of the surrounding earth 

 permitted. All this astonishing amount of movement has 

 been going on year after year since the time when, as a 

 seedling, the tree first emerged from the ground." 



Practical Studies. — (a) Soak a few beans in water, and when the 

 little roots begin to protrude pin the beans carefully to a weighted 

 cork under a bell-jar, and observe the movements of the radicles. 



(6) Germinate and study in like manner the seeds of cabbage, rad- 

 ish, Indian corn. 



(c) Fix a slender filament of glass to the rapidly growing end of a 

 shoot of fuchsia, geranium, or verbena (using a drop of thick shellac- 

 glue), and observe the circumnutation. If a plate of glass be laid 

 horizontally just above the tip of the glass pointer, the movements of 

 the latter may be readily recorded by lines or dots ou the glass. Or 

 a microscope may be fixed in such a position that the tip of the pointer 

 is in focus, when the movement will be made visible to the eye. 



((i) Fix a glass pointer to the tip of a leaf of a suitable plant (as a 

 fuchsia, geranium, primrose, etc., grown in a pot) and record the 

 nutations on a glass plate fixed vertically or horizontally in such a 

 way as to be approximately at right angles to the pointer. 



186. Geotropism. — Under this is included all those 

 movements of plants or their parts due directly or indi- 



