2o6 Education through Nature 



ture is present. This moisture has come down, per- 

 haps, as rain; and, percolating down through the soil, 

 it has come into contact with various salts and gases 

 carbon dioxide, nitrogen, and others variously com- 

 bined. These have been dissolved, more or less, and 

 have entered into the water as solutions (Experiment I). 



The roots, with their root-hairs, like tiny tubes 

 spread out in the soil, coil around pebbles and sand- 

 grains, and by a process of osmosis (Experiment VIII) 

 drink up the water with its dissolved substances, 

 much as blotting-paper takes up a drop of spilt ink 

 (Experiment VI). 



The water then rises through the stem (Experiment 

 III) partly because of root-pressure, due to osmosis 

 (Experiment VIII), and partly by capillary attraction, 

 as in the experiment with the filter-paper. In this 

 way the water is carried up to the leaves, being 

 prevented from oozing out from the side of the stem 

 by the outer layer surrounding the stem like a skin 

 (Experiment X). This cuticle is impervious to water, 

 as can be seen in the experiment with the cork 

 (Part I, Chapter IV, Section XIII). 



Transpiration. The leaves, being spread out, offer 

 a large surface, from which evaporation can take place. 

 But they, too, are covered with cuticle. On the under 

 side of the leaf, however the side usually turned away 

 from the source of light there are numerous pores or 

 openings in the cuticle, so constructed that they close 

 and open according to the dampness of the atmosphere. 

 These pores are called stomata. They allow air to 

 enter, which, coming in contact with the water in the 

 stem and leaf, becomes laden with the moisture which 

 entered the root from the soil, and carries it away some- 

 what as vapor or perspiration is carried away from 

 our skin (Experiment IX). 



Respiration. Air enters the soil around the roots 

 of the plant when the soil > is well stirred. The farmer 



