50 FOUNDATIONS OF BOTANY 



place mainly through the root-hairs, which the student has 

 examined as they occur in the seedling plant, and which 

 are found thickly clothing the younger and more rapidly 

 growing parts of the roots of mature plants. Some idea 

 of their abundance may be gathered from the fact that on 

 a rootlet of corn grown in a damp atmosphere, and about 

 one-seventeenth of an inch in diameter, 480 root-hairs have 

 been counted on each hundredth of an inch of root. The 

 walls of the root-hairs are extremely thin, and they have 

 no holes or pores visible under even the highest power 

 of the microscope, yet the water of the soil penetrates 

 very rapidly to the interior of the root-hairs. The 

 soil-water brings with it all the substances which it can 

 dissolve from the earth about the plant ; and the close- 

 ness with which the root-hairs cling to the particles of soil, 

 as shown in Figs. 11 and 21, must cause the water which 

 is absorbed to contain more foreign matter than under- 

 ground water in general does, particularly since the roots 

 give off enough weak acid from their surface to corrode 

 the surface of stones which they enfold or cover. 



62. Osmosis. The process by which two liquids sep- 

 arated by membranes pass through the latter and mingle, 

 as soil-water does with the liquid contents of root-hairs, is 

 called osmosis. 



It is readily demonstrated by experiments with thin 

 animal or vegetable membranes. 



EXPERIMENT XV 



Osmosis as shown in an Egg. Cement to the smaller end of an egg 

 a bit of glass tubing about six inches long and about three-sixteenths 

 of an inch inside diameter. Sealing-wax or a mixture of equal parts 

 of beeswax and resin melted together will serve for a cement. 



