STRUCTURE AND PHYSIOLOGY OF PLANTS 15 



mingle with the contents of root-hairs. The thin liquid 

 passes more rapidly. Osmosis may be well illustrated in a 

 number of ways. 



Exercise. — Osmosis with Potato, — Take a wilted potato 

 tuber and cut it into shces about one-fourth inch thick. 

 Place a few slices in water. They become more rigid in an 

 hour or so because of the water taken into the cells. Place 

 a few slices in strong salt water. They become more 

 flaccid or wilted because of the water drawn from them into 

 the brine. The potato sap is naturally denser than water, 

 but not so dense as the salt water. 



Exercise. — Osmosis with an Egg. — In the small end of 

 an egg make a hole a little larger than a pin head. Over 

 this hole fasten a short piece of glass 

 tubing. Melted paraffin or wax will 

 fasten it well. At the large end of the 

 egg chip away a bit of the shell. Place 

 it with the large end down in the wide 

 mouth of a bottle which is full of 

 water (Fig. 6). After several hours 

 liquid will be seen to rise in the tube, 

 evidently caused by water making its 

 way through the thin membrane lining 

 the egg-shell. This membrane shows 

 no pores even under the microscope. 



Plant=food from Soil. — If plants 

 take about ninety-five per cent of their 

 food from the air there is left only 

 about five per cent to be obtained from 

 the soil. The plant-food from soils 

 must be in soluble form, and is taken 

 in with the soil water. When plant-food is soluble it can 

 pass through the membrane of the fine root-hairs growing 

 on the roots of plants. It produces in the plant the part 

 of the tissue tvhich is called the ash or mineral matter. 



Fig. 6. — Osmosis with 

 an egg over a bottle of 

 water. The egg liquid and 

 the water exchange places 

 through the membrane of 

 the egg. Water moves the 

 faster and soon fills the 

 shell to overflowing. 



