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. 
(b) 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 Fic. 54.—Photo- 
below and the cotyledons above. Put the ¢yP*™°*Ppemment 
cork in a bottle so that the tip of the root 
dips into water, or better still, into a nutrient solution (see 
9 
