IRRITABILITY. 07 



EXPERIMENT 83. 



WARPING OF WOOD. 



Wipe the adhering moisture from a thin piece of wood, such as 

 a cigar-box lid, which has lain in water 24 hours, and fasten to 

 another piece of similar size which is air-dry, by means of a number 

 of small nails. Lay in a dry place. The loss of moisture from the 

 saturated piece will cause the double board to become curved. 



Note the " warping " of unseasoned timbers. 



EXPERIMENT 84. 



MOVEMENTS OF FRUIT-CAPSULE OF IMPATIENS. 



Bring some fruit of Balsamina (Impatiens noli tangere) which 

 is nearly ripe into warm dry air. (Hold 

 at a distance above a gas-flame.) The 

 outer covering of the fruit contracts and 

 forcibly ejects the fruit. Make sections 

 of the portions of the capsule, and describe 

 the action of the hygroscopic cells. 



EXPERIMENT 85. 



TWISTING MOVEMENTS OF THE BEAK OF AN 

 ERODIUM SEED. 



Erodium seed with the long 

 beak twisted by drying. A moist seed of Erodium is placed 



with the point in a damp soil. In drying 



the beak curves and twists in a spiral form. If the twisting of the 

 beak is hindered by a piece of wood thrust into the sand beside it,, 

 the force will be exerted upon the seed, and will be thrust into the 

 sand still deeper. (Fig. 63.) 



