36 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS 



needle into tlie root at the level of the mercury (to mark the exact level), 

 withdraw the root, and measure the length of tlie part submerged in mercury. 

 To see whether this part would have stayed under by virtue of its own weight, 

 cut it off and lay it on the mercury. Push it under with a pair of steel for- 

 ceps and then let go of it. What does it do ? 



EXPERIMENT XIX 



What causes the root to go downward ? 



A. Pin some soaked Windsor beans to a large flat cork, cover them with 

 thoroughly moistened chopped peat moss, and cover this with a thin 

 glass crystallizing dish. Set the cork on edge. 



B. Prepare another cork in the same way, attach it to a clinostat, and 

 keep it slowly revolving in a vertical position for from three to five 

 days. Compare the directions taken by the roots on the stationary and 

 on the revolving cork. 



Rekkrences. Ganong, 10 ; Pfeffer-Ewart, 31, III. 



22. Propagation by means of roots. Bury a sweet potato or a 

 dahlia root in damp sand and watch the development of sprouts 

 from adventitious buds. One sweet potato will produce several 

 crops of sprouts, and every sprout may be made to grow into a 

 new plant. It is in this way that the crop is started wherever 

 the sweet potato is grown for the market. 



SOME PROPERTIES OF CELLS AND THEIR 

 FUNCTIONS IN THE ROOT 



EXPERIMENT XX 



Osmosis as shown in an egg. 



A. Cement to the smaller end of an egg a bit of glass tubing about six 

 inches long and about three sixteenths of an inch in inside diameter. A 

 mixture of equal parts of beeswax and rosin melted together makes 

 the best cement for this. Chip away part of the shell from the larger 

 end of the egg, place it in a wide-mouthed bottle or a small beaker full 

 of water (as shown in Principles, Fig. 28), and then very cautiously 

 pierce a hole through the upper end of the eggshell by pushing a 

 knitting needle or wire down through the glass tube. AVatch the 



