288 THE REASON WHY. 



1 The heavens declare the glory of God : and the firmament showeth his handj 



work. Day unto day uttereth speech, and night untq night showeth 



knowledge." Ps AJLM xix. 



the air, by night, but, on the contrary, give off carbonic acid gas. Therefore il 

 has been stated that plants in rooms by night are unhealthy. Mr. Robert 

 Hunt, one of the ablest chemists of the present time, makes the following 

 remarks upon this subject in his " Poetry of Science :" 



" The power of decomposing carbonic acid is a vital function which belongs 

 to the leaves and bark. It has been stated, on the authority of Leibig, that 

 during the night the plant acts only as a mere bundle of fibres that it allows 

 of the circulation of carbonic acid and its evaporation, unchanged. In his 

 eagerness to support his chemical hypothesis of respiration, the able chemist 

 neglected to enquire if this was absolutely correct. The healthy plant never 

 ceases to decompose carbonic acid during one moment of its existence ; but 

 during the night, when the excitement of light is removed, and the plant 

 reposes, its vital powers are at their minimum of action, and a much less 

 quantity is decomposed than when a stimulating sun, by the aciion of its rays, 

 is compelling the exertion of every vital function." 



In hot, swampy countries, where vegetation is very rapid, and the soil loaded 

 with decomposing carbonic matter, the plants absorb more carbonic acid than 

 they require, and they then evolve carbonic acid gas from their leaves. Hence 

 such climates as the West Indies are injurious to life, though favourable to 

 vegetation. 



1147. How do plants obtain hydrogen ? 



They obtain liydrogen in combination with oxygen in water, and 

 with nitrogen, in the form of ammonia, as which it exists in animal 

 manures. 



1148. How do plants obtain nitrogen ? 



From the atmospheric air, and from the soil, in which it is 

 combined with other elements. 



1149. How do plants apply these elements to the formation 

 of their own structures? 



When those substances which form the food of plants are absorbed, 

 either by their leaves or their roots, they are converted, with the 

 aid of water, into a nutritive sap, which answers the same purposes 

 in plants as blood does in animals. 



1150. How is the nutritive sap applied to the growth and 

 enlargement of the plant f 



Every seed contains a small amount of nutrition, sufficient for the 

 sustentation of the germ of the plant, until those vessels are 

 formed, by which the nutritive elements can be absorbed and used 

 for the further development of the living structure. 



The earth, penetrated by the sun's rays, warms the sleeping 

 germ, and quickens it into life. For a short time the germ lives upon 



