48 PLANT BIOLOGY 



out till it wilts ; then add water and note the rapidity with which 

 it recovers. Vary the experiment in quantity of water applied. 

 Does the plant call for water sooner when it stands in a sunny win- 

 dow than when in a cool shady place? Prove it. 39. Immerse 

 a potted plant above the rim of the pot in a pail of water and let 

 it remain there. What is the consequence ? Why ? 40. To test 

 the effect of temperature on roots. Put one pot in a dish of ice 

 water, and another in a dish of warm water, and keep them in a 

 warm room. In a short time notice how stiff and vigorous is the 

 one whose roots are warm, whereas the other may show signs of 

 wilting. 41. The process of osmosis. Chip away the shell from 

 the large end of an egg so as to expose the uninjured membrane 

 beneath for an area about as large as a dime. With sealing-wax, 

 chewing-gum, or paste stick a quill about three inches long to 

 the smaller end of the egg. After the tube is in place, run a 

 hat pin into it so as to pierce both shell and membrane ; or use 

 a short glass tube, first scraping the shell thin with a knife and 

 then boring through it with the tube. Now set the egg upon the 

 mouth of a pickle jar nearly full of water, so that the large end 

 with the exposed membrane is beneath the water. After several 

 hours, observe the tube on top of the egg to see whether the water 

 has forced its way into the egg and increased its volume so that 

 part of its contents are forced up into the tube. If no tube is at 

 hand, see whether the contents are forced through the hole which 

 has been made in the small end of the egg. Explain how the law 

 of osmosis is verified by your result. If the eggshell contained 

 only the membrane, would water rise into it? If there were no 

 water in the bottle, would the egg-white pass down into the bot- 

 tle ? 42. The region of most rapid growth. The pupil should 

 make marks with waterproof ink (as Higgins' ink or indelible 

 marking ink) on any soft growing roots. Place seeds of bean, 

 radish, or cabbage between layers of blotting paper or thick cloth. 

 Keep them damp and warm. When stem and root have grown 

 an inch and a half long each, with waterproof ink mark spaces 

 exactly one quarter inch apart (Figs. 48, 49). Keep the plantlets 

 moist for a day or two, and it will be found that on the stem some 

 or all of the marks are more than one quarter inch apart ; on the 

 root the marks have not separated. The root has grown beyond 

 the last mark. 



Note to Teacher. — The microscopic structure of the root can 

 be determined only by the use of the compound microscope ; but 

 a good general conception of the structure may be had by a care- 

 ful attention to the text and pictures and to explanations by the 

 teacher, if such microscopes are not to be had. See note at close 

 of Chapter X. 



