370 LIFE ON THE EARTH 



only do roots absorb the water from the soil, but they se- 

 crete weak acids which aid in dissolving the mineral sub- 

 stances which the plants need. This can be seen where 

 plant roots have grown in contact with polished surfaces, 

 such as marble. These surfaces are found to be etched. 



Experiment 111. Cut a potato in two. Dig out one of the 

 halves into the shape of a cup and scrape off the outside skin. 

 Fill the potato cup about f full of a strong solution of sugar. Mark 

 the height of the sugar solution by sticking a pin into the inside of 

 the cup. Place the cup in a dish of water. The water should 

 stand a bit lower than the sugar solution in the potato 

 cup. After the cup has stood in the water for some 

 time, notice the change in the height of the denser 

 sugar solution. 



Experiment 112. Bore a f-inch hole 3 or 4 inches 

 deep in the top of a carrot. Scrape off the outside 

 skin and bind several strips of cloth around to keep 

 the carrot from splitting open. Fit the hole with a 

 one-hole rubber stopper having a glass tube about 1 

 meter long extending through it. (Figure 109.) Fill 

 the hole in the carrot with a strong sugar solution 

 colored with a little eosin and strongly press and tie 

 in the stopper. The sugar solution will be forced a 

 short distance up the tube by the insertion of the stopper. Mark 

 with a rubber band the height at which it stands. Submerge the 

 carrot in water and allow it to stand for a few hours. Mark 

 occasionally the height of the column in the tube. Taste the 

 water in which the carrot was submerged. There has been an 

 interchange of liquids within and without the carrot. 



The plant root takes up its water in the same way the 

 water was taken into the sugar solution of the potato cup 

 or of the carrot. The water or sap within the substance 

 of the root is denser than the soil water, just as the sugar 

 solution was denser than the water outside. It has been 

 found that whenever two liquids or gases are separated 



