lO EXPERIMENTAL PLANT PHYSIOLOGY. 



7. Condition of Nutrient Substances. — Only liquid nutriment 

 is taken up by the roots. The mineral substances of the soil 

 are slowly dissolved by percolating water which contains small 

 amounts of oxygen and carbon dioxide, as well as traces of 

 nitric and sulphuric acids derived from the air. In some cases 

 the walls of the root-hairs are saturated with an acid sap, 

 which aids in the solution of the mineral salts. 



EXPERIMENT 8. 



ACIDITY OF ROOTS. 



Place the roots of a seedling of Pea, Bean, or Corn grown in a 



germinator, on a sheet of blue litmus 

 paper. The portion of the paper 

 touched becomes red, indicating the 

 presence of an acid. 



EXPERIMENT 9. 



CORROSIVE ACTION OF ROOTS. 



Fill a s-inch pot half full of 

 moist loam. On this lay a piece of 

 marble whose upper surface is highly- 

 polished. Fill the pot with moist 

 sand and imbed a germinated pea 

 or bean near the surface. After the 



soil has been thoroughly penetrated 

 Marble plate«>rroded by roots. ^^ ^^^ ^^^^^ (^^ ^^ ^^ ^^y^) ^^^^ 



out the marble plate, dry, and by re- 

 flected light note the rough lines etched on its upper surface by the 

 acid of the roots. 



8. Nutrition of Parasitic Plants. — Many plants of which 

 Mistletoe and Cuscuta are examples do not develop a root 

 system for the absorption of nutriment from the soil, but 

 attach themselves to the bodies of other plants, from which 

 they derive sap containing the necessary substances already 

 prepared. Such plants are termed parasites. In many cases 

 parasitic plants are entirely devoid of chlorophyll and depend 

 altogether on the host-plant for their food. Cuscuta (Dodder), 



