344 CHEMISTRY. 



for the oxygen, as you saw in 142. But in the plant the 

 decomposition is effected in the most quiet manner, and the 

 two elements thus separated are united with carbon in the 

 production of a great variety of substances. 



476. Plants Growing Without Earth. You can now under- 

 stand how it is that plants often grow in water only. It 

 is because the air furnishes the carbon, while the water 

 furnishes the oxygen and hydrogen, and these are all the 

 elements which are absolutely necessary for the structure 

 of the plant. We have familiar examples in the hyacinths 

 raised in bulb glasses, in oats growing from seeds on cot- 

 ton floating in water, and in canary-seed throwing up del- 

 icate shoots from all parts of a pine-cone which stands im- 

 mersed in water in a glass. There is, it is true, in all these 

 cases some nitrogenous matter in the seeds, and also in the 

 water, unless it be freed from its impurities by distillation. 

 But this is too small in amount to satisfy the natural de- 

 mands of the plant, and therefore, though there be growth, 

 there is by no means that vigorous and productive growth 

 that there would be if all the materials naturally belonging 

 to the plant were at hand. The oats and canary-seed, there- 

 fore, produce no seeds, or very defective ones, and the hya- 

 cinth produces no additional bulb. And, farther than this, 

 in the case of the oats and canary-seed the growth is very 

 manifestly deficient, because the plants are naturally rich in 

 nitrogen, and therefore especially require that article of diet, 

 as we may express it, which is not true of the hyacinth. 



477. Sources of the Nitrogen in Plants. Although nitro- 

 gen is not needed, so far as the structure of plants is con- 

 cerned, it is generally present in some amount ; and it is 

 essential to the formation of the fruits of many plants, as 

 the grains, beans, pease, etc. From whence does it come ? 

 There is an abundance of it in the air, for four fifths of the 

 atmosphere is nitrogen. And it is not combined with any 



