39 2 APPENDIX. 



rated with moisture and measure after i hour. Compare meas- 

 urements. (If elder is not at hand use young shoots of grape, 

 wild or cultivated.) 



Br Split a scape of dandelion lengthwise with a sharp knife 

 into four strips. Note immediate effect upon their form. Lay 

 the strips in water for a few minutes. Observe form. Transfer 

 them to 5 per cent, salt solution. What effect? What causes 

 these changes of curvature? (The young stems (hypocotyls) of 

 castor bean may be substituted for dandelion scapes but are not 

 so responsive.) 



4. To show the existence of transverse tensions of tissues due to 

 unequal growth. 



A. From a piece of willow or poplar stem separate a ring of 

 bark 1 cm. wide, slitting it on one side only, taking care not to 

 stretch it. Keep it in a moist atmosphere for a few minutes, 

 and then replace it. Does it meet about the wood ? 



B. Cut a slice about 2 mm. thick from the end of a stalk of 

 rhubarb. Bisect this and keep the halves for a few minutes in a 

 moist atmosphere, then place severed edges together. Do they 

 touch throughout? 



5. To show the location of root hairs and especially their adhesion 

 to soil particles. H~^[ 79, 200.) 



Germinate wheat in sand and when seedlings have several 

 strong roots dig up carefujly; shake sharply in water; note 

 where soil clings most tenaciously. Brush away most of this 

 with camelhair brush and examine a bit of this part of root under 

 a low power of microscope. Observe distortion of root hairs, 

 and particles of sand partly embedded in them. 



6. To show excretion of acid salts by roots. (^[ 202.) 



Fill a wide-mouthed bottle holding 250 cc. with tap water; add 

 2-3 drops of ammonia and several drops of phenolphtalein.* 

 If the water does not now remain pink add a drop or two more of 

 ammonia. Select a vigorous seedling bean grown in sawdust; 

 rinse roots well to remove impurities. 



Cut in two a cork which fits the bottle; in the halves cut two 

 corresponding notches of such size that with a little cotton for 

 packing the plant will be firmly held. Place the plant with 



* An indicator for acids, colorless when a fluid in which it is dissolved is acid, rose 

 pink or darker when alkaline. For use the crystallized phenolphtalein is dissolved in 

 alcohol. 



