MODE OF DIFFUSION OF GASES INTO WATER. jg 



mals ; for animal life, though carried on beneath the surface of this liquid medium, has 

 the same chemical object in view as when carried forward on the surface of the earth ; 

 it ends in the conversion of carbon into carbonic acid, of hydrogen into water, and an 

 evolution of heat. Its oxygen, in the same manner, has two sources of supply, direct 

 absorption from the air, as in the former instance, and a still more concentrated store 

 in those little air-bells that cover the green vegetable matter as long as the sun is shi- 

 ning; in these the volume of oxygen is, on an average, double that of the nitrogen. 

 Upon them the water exerts its solvent powers, removes as much as it can carry away, 

 and the bubble then floats to the top of the water, and escapes out into the air. From 

 the same two sources nitrogen is also procured. With these abundant supplies, there- 

 fore, furnished partly from the vital changes which are taking place in its mass, and 

 partly from the external air, the constitution of the water-atmosphere is kept up unim- 

 paired. 



53. All the carbon which we thus find in the green matter comes from dissolved car- 

 bonic acid, all the hydrogen from water or ammonia ; the latter also furnishes a cer- 

 tain quantity of nitrogen, other portions of which are obtained, without any decompo- 

 sition, from that which has been dissolved out of the atmosphere. The general prin- 

 ciples of life carried on in the water are modelled on the same idea as in the case of 

 life carried on in the air. In both cases, vegetables act as the great formative agents, 

 and animals as the destructive power; and in both, the source and origin of action is 

 to be found in the beams of the sun. For nearly two centuries, physical science has 

 fully admitted the agency of that central star as the great seat of mechanical force, 

 which retains the different planets in their orbits. It is only of late years that we are 

 beginning to recognise his agency as the author of organization and life, who lays up, 

 with an almost provident foresight, in vegetable productions, stores of light and heat 

 for the use of the animal world. The coal-fields which furnish us with fuel are the re- 

 mains of primeval forests, among the branches of which birds nestled at night ; and the 

 warmth that we receive from them, and the light that they give us, have been safely 

 stored up for us for thousands of centuries. Those little insects, also, which at certain 

 seasons cause the sea to shine with a phosphorescent light, derive their glow remotely 

 from the vegetable kingdom ; and the fireflies, which, in such countless multitudes, on 

 a summer evening in Virginia, make the grass and trees glitter with their intermitting 

 beams, are only pouring forth again rays which once came from the sun. 



54. I have thus far considered the process of evolving green matter from a primitive 

 cell or seed placed under water. It is now proper to generalize on these views, and to 



show that, so far from this being an insignificant case, it represents fully all that goes on 

 in the vegetable tribes, whether they live under the water or in the air. Let us, therefore, 

 proceed at once to investigate what takes place in the case of plants which are of a 

 more complex character, and higher in the scale of creation. If a few garden seeds of 

 any kind are sown in a flower-pot, and caused to germinate in a dark room, after a 

 while it will be perceived that they can grow for a certain space in the absence of light; 

 their young leaves, if any should be put forth, are of a yellow or gray- white colour, and 

 they soon fade away and die. But if these plants be brought out into the light, they 



