ROOTS. 35 



weight of water. Grasses have been known to take in their 

 weight of water in every twenty-four hours of warm, dry 

 weather. This absorption takes 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 gath- 

 ered from the fact that on a rootlet of corn grown in a damp 

 atmosphere, and about ^j inch in diameter, 480 root-hairs 

 have been counted on each hundredth of an inch in length. 

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

 free from any holes or pores which can be seen even by 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 closeness 

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

 shown in Fig. 19, must cause the water which is absorbed 

 to contain more foreign matter than underground 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. 



51. Osmose. — The process by which two liquids separated by 

 membranes pass through the latter and mingle is called osmose. 



62. Experiment 15.* Osmose in an Egg. — Cement to the smaller 

 end of an egg a bit of glass tubing about six inches long and about ^-g 

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

 wax and rosin melted together will serve for a cement. 



Chip away part of the shell from the larger end of the egg, place it in 

 a wide-mouthed bottle or a small beaker full of water, as shown in 

 Mg. 21, then very cautiously pierce a hole through the upper end of the 

 egg-shell by pushing a knitting-needle down through the glass tube. 



Watch the apparatus for some hours and note the gradual rise of the 

 contents of the egg in the tube.i 



1 Testing the contents of the beaker with nitrate of silver solution will then show 

 the presence of a little common salt in the water. 



