THE AIR 19 



though no one can discern any difference in the living matter of the two. 

 Each follows the laws of its inheritance, and obeys the order set out for it in 

 creation. 



I have said that this living matter inside the plant cells is partly of a 

 granular nature. Some of these grains are colored green, and thus give us 

 the green color of vegetation. This green color is a very important matter, 

 for without it there could be no growth. We may put a plant in darkness 

 and blanch the leaves white, and then examine the grains under the micro- 

 scope and we find that they are still there, but the green color is gone, and the 

 plant stops growing. It is evident then that the green is of importance to the 

 growth of the plant. It is, in fact, the substance that enables the plant to get 

 the food it needs from the carbon-di-oxide in the air. 



Every leaf has on its surface a mutitude of small valves, opening and 

 closing like a pair of lips, and they are really the mouths through which it 

 takes in food. These mouths are far more plentiful on the under sides of 

 leaves than on the upper, and in some plants there are none at all in the upper 

 surface. The interior of the leaf is made up of a loose aggregation of cells 

 containing the green granules. The mouths open in among the spaces be- 

 tween these loosely arranged cells, and thus bring the air to the interior of 

 the leaf. When the sun is shining, and at no other time, these mouths in 

 the leaf are wide open. The air enters the leaf laden with the carbon-di-oxide. 

 If the temperature around is proper for the growth of that particular plant, 

 the green -matter at once decomposes the carbon-di-oxide, separating the car- 

 bon from the oxygen. The oxygen is then thrown off to purify the air, and 

 the carbon is retained by the plant. We do not know that this identical 

 oxygen is that which is thrown off, but we do know from experiment that the 

 same amount of oxygen is thrown off as was combined with the carbon. 



Now in the wonderful laboratory of the green leaf, begins the work of the 

 living matter. From the roots water has been brought up to the leaves, in 

 which is dissolved the various forms of plant food that come from the soil. 

 As it comes from the roots it is merely water with plant food dissolved in it. 

 With this water, and the carbon that has been gotten from the air through the 

 leaf mouths, the living matter goes to work to prepare food for its own suste- 

 nance, and to make the materials out of which it builds its cell walls, and 

 thickens their woody structure. The first thing formed from the carbon, 

 hydrogen and oxygen, is probably some form of sugar for the immediate use 

 of the plant. But the living matter works rapidly, and makes more material 

 than it can use at once, either for food or building walls, and hence it has to 

 store the reserve material. This reserve material is the first thing we can dis- 

 cover in the leaf, and it is starch. When starch is made in the leaf it is soon 



