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by innumerable minute pores on the surface of the leaves 

 and green shoots specially constructed for the purpose. 

 These pores are so small that they require a strong lens to 

 show them, yet they are wonderfully constructed. They 

 are not permanent openings, but each has a pair of lips 

 which are capable of opening or closing just as the lips 

 of a mouth. When exposed to light the lips open and the 

 moisture within the tissues can freely evaporate through ; 

 when the light fails the lips close together and stop the 

 process. These little pores, from their peculiar structure 

 and function, have received the name of stomata, which 

 means mouths. Each is a stoma. A stoma has another 

 function equally as important to a plant as allowing the 

 escape of moisture, namely, to allow the passage inwards 

 of air. If you take a plant and thoroughly dry it its 

 weight is reduced very considerably. Now, if it is baked 

 at a considerable heat, but not burnt, it- will turn black, 

 or, as we may say, turns into charcoal. Chemists call 

 charcoal carbon. By far the greater portion of the dry 

 part of a plant is carbon. A plant absorbs practically no 

 carbon through the roots ; it is all procured from the 

 atmosphere, which enters the green parts through the 

 stomata. As there are on the average only four parts of 

 a gas containing carbon in ten thousand parts of air, it 

 can well be imagined what a quantity of atmosphere must 

 in a year pass in and out of the stomata of a tree to sup- 

 plv its yearly wants. 



The carbon of a plant is first reduced from the carboruc 

 acid of the air and then built up by a complicated process 

 with molecules of water to form complex substances in the 

 green tissue : these first appear to us in the form of starch 

 or sugar. This is afterwards used up by the plant to form 

 its multitudinous compounds, or as fuel, to supply energy 

 for growth. What we want to note here is that this 

 marvellous building up of substance only takes place in 

 the green tissue of plants. As all familiar plants are 

 green, we generally take the colour as a matter of course, 

 but it is worthy of the most grave consideration. The 

 green colour is due to a definite substance, plant-green. 

 This substance has the power, when light is suffiicently 

 intense, of splitting up carbonic acid and forming starch 

 or sugar, from which the higher compounds are then 

 formed. Plant-green is the only known substance that has 

 this power. Wherefore not "only all plants, but also 

 animals, depend for their existence upon the action of the 

 green tissue of plants. 



