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. 



EXERCISES. Osmosis with Potato. Take a wilted potato 

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

 Place a few slices in water. Do they become more rigid 

 in an hour or so? Is water taken into the cells? Place 

 a few slices in strong salt water. Should they become 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). Watch later and if liquid be 

 seen to rise in the tube, give its source. 

 Can water make its way through the 

 thin membrane? 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 which is called the ash or mineral 

 matter. 



FIG. 6. Osmosis with 

 an egg over a .bottle of 

 water. If egg liquid and 

 the water exchange places 

 through the membrane 

 of the egg, which moves 

 the faster? Why does fluid 

 rise in tube? 



