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. 
