NASTIC MOVEMENTS 129 



growth on one or the other side of the base of the petiole. 

 Such responses to changes in light and temperature cease 

 when the leaves have attained full growth, while those 

 due to turgor changes in the leaves that have pulvini 

 persist. 



Laboratory Studies, (a) Fix a slender filament of glass or a 

 stiff bristle to the rapidly growing end of a shoot of Fuchsia, 

 geranium (Pelargonium), or verbena, using a drop of thick 

 shellac glue. Support a plate of glass in a horizontal position, 

 just above the tip of the pointer, and record, by making ink 

 dots on the glass, the position of the pointer at definite inter- 

 vals of time, say every ten minutes. A microscope may be 

 focused upon the tip of the pointer and the movement observed 

 in this way. In this and similar experiments the illumination 

 should be as nearly equal as possible on all sides. 



(6) In a similar manner, the nutatory movements of a leaf 

 may be observed by fastening a pointer to its tip, and observing 

 it with a horizontal microscope or by recording the position of 

 the pointer at successive intervals on a vertical glass plate. 



(c) Nutation can be demonstrated also in the long stout 

 roots from seedlings of beans, peas, etc. These should be 

 placed so as to point directly downward, so as to avoid geo- 

 tropic curvature. The movement can be observed by placing 

 a mirror at an angle of 45 degrees under the tip, and focusing a 

 horizontal microscope on the tip as reflected in the mirror. 



(d) Observe the rotatory movements of the horizontally 

 bent end of a shoot of morning-glory (Ipomoea) or hop (Humu- 

 lus). Note the time required to make a complete revolution. 

 The stem also must twist one whole revolution 



for every turn the tip makes. Place an upright 

 stake in the way of the shoot, and note how the 

 climbing takes place. 



(e) Germinate a mustard or sunflower seed 

 in the dark, and after the cotyledons have 

 escaped from the seed coat, place the seedling 



in a hole in a cork, so that the root projects FIG. 54. Photo- 

 below and the cotyledons above. Put the gP' sme *P eri 

 cork in a bottle so that the tip of the root 

 dips into water, or better still, into a nutrient solution (see 

 9 



