TUBERS AND BULBS 47 



C. Note the little scale overhanging the edge of the eye, and 

 see if you can ascertain what this scale represents. 



D. Cut the potato across, and notice the faint broken line 

 which forms a sort of oval figure some distance inside 

 the skin. Place the cut surface in eosin solution, allow the 

 potato to stand so for many hours, and then examine, by 

 slicing off pieces parallel to the cut surface, to see how far 

 and into what portions the solution has penetrated. Refer 

 to the notes on the study of the parsnip (Sec. 21), and see 

 how far the behavior of the potato treated with eosin solu- 

 tion agrees with that of the parsnip so treated. 



E. Cut a thin section at right angles to the skin, and examine 

 with a high power. Moisten the section with iodine solution 

 and examine again. 



F. If possible, secure a potato which has been sprouting in a 

 warm place for a month or more (the longer the better), and 

 look near the origins of the sprouts for evidences of the loss 

 of material from the tuber. 



EXPERIMENT XXIV 



Use of cork.* * Carefully weigh a potato ; then pare another 

 larger one, and cut portions from it until its weight is made 

 approximately equal to that of the first one. Expose both freely 

 to the air for some days and reweigh. What does the result show 

 in regard to the use of the corky layer of the epidermis? 



34. Structure of a bulb; the onion. 



A. Examine the external appearance of the onion, and observe 

 the thin membranaceous skin which covers it. This skin 

 consists of the broad sheathing bases of the outer leaves 

 which grew on the onion plant during the summer. Remove 

 these and notice the thick scales (also formed from bases of 

 leaves) which make up the substance of the bulb. 



B. Make a transverse section of the onion at about the middle, 

 and sketch the rings of which it is composed. Cut a thin 



