4° BOTANY. 



away the root hairs, we find that small particles cling so 

 tenaciously to the root hairs that they are not removed. 

 Placing a few such root hairs under the microscope it appears 

 as if here and there the root hairs were glued to the minute 

 soil particles. 



In soil most suitable for the growth of land plants the water is 

 not in excess. It is in the form of a thin film surrounding the 

 soil particles. Some of the soil particles being "glued" to 

 the root hairs, this portion of the water film is brought into 

 close contact with the root hairs so that it can be absorbed. 

 Plants cannot remove all the water from the soil. 



Note. — Some plant food is in solution in the water of the soil, but much 

 of it is in an insoluble form (minute particles, or rocks, containing mineral 

 substances), or in the form of organic matter (as leaves, stems, or other plant 

 parts, or animal matter). The organic matter in the soil is in process of 

 decay because certain microscopic fungi, and especially bacteria, feed upon 

 it and change some of it into a form which can be taken up as food by the 

 higher plant. The insoluble particles, containing mineral substances, are 

 constantly being corroded by the action of certain acids, especially carbonic 

 acid, which is constantly being formed in the soil. The walls of the root hairs 

 are also saturated with this acid, and thus they are able to dissolve some of 

 these mineral substances. This corroding action of the roots can be well 

 shown by placing a small marble plate in a pot; then plant beans or peas on 

 the plate, and cover with earth. In lieu of the marble plate the peas may be 

 planted in clam, or oyster, shells, which are then buried in the soil of the 

 pot, so that the roots from the seedlings will come in contact with the smooth 

 surface of the shell, or of the marble if that is used. After the plants have 

 been growing two or three weeks, remove the soil, and wash the surface of 

 the marble or shell. Hold the surface now toward the window in such a 

 way as to see the light reflected from the surface. The surface has been 

 etched by the action of the roots. 



Demonstration 1 5 (or Exercise). 



78. Plants can obtain water from soil which appears dry. — Use small pots 

 with well-grown seedlings. Place the pots in a dry room. Supply no water 

 to the soil. From day to day observe the condition of the soil, and feel of it 

 to note the condition of dryness. Can plants live and grow in a soil which 

 looks and feels dry ? 



When the plants have wilted remove them from the soil. Weigh the pot 

 of soil. Then place it in an oven and bake it. Weigh again. Has it lost 



