REQUIREMENTS OF PLANTS. 41 



of it than is necessary to convert the hydrogen into water ; thus these 

 have aa excess of hydrogen. Nitrogen is a part of vegetable albu- 

 men, giuten and of the acids. It forms but a small proportionable 

 part of the weight of plants, yet it is always present in some part. 

 The juices of all plants contain organic acids, generally combined with 

 metalic oxides, which are found in the ashes of plants. 



A plant requires, then, for its growth, such substances as contain 

 carbon and nitrogen, or which are capable of yielding these two ele- 

 ments for its organization; and also water, or its two elements, 

 oxygen and hydrogen ; and finally, a soil is required which will furnish 

 the plant with the metalic oxides, or inorganic bases. 



Each, genus of plants requires special conditions for their life ; and 

 individuals require many conditions : they cannot be brought to matu- 

 rity, indeed, if but one of these be wanting. Their organs, like those 

 of animals, contain substances of very different kinds; and in all are 

 found metalic salts. For the production of all their organs, therefore, 

 their food must contain all their elements. These may be united in 

 one substance, or they may exist in several. 



Vitality in each organ is the power it possesses at all times of re- 

 producing itself; hence it requires substances containing those com- 

 posing itself and capable of transformation. When this is not the case, 

 or the food is too great, or exerts a peculiar chemical action, as with 

 poisons, the organ is changed. The most nutritious food may cause 

 death, and hence the importance of considering every quality of their 

 food. Other substances are also required, such as common salt, so 

 essential to animal life ; and metalic compounds are equally essential 

 to the life of plants. But, before we can understand or administer 

 nutriment to the plant, it is necessary to become acquainted with the 

 nature of the soil it grows in, and of air and rain water. 



Vegetables depend on the atmosphere for much of their support and 

 vital energy. The chemical constituents of this are known to be the 

 two gases, oxygen and nitrogen, in the proportions of 23.1 of oxygen 

 to 76.9 of nitrogen, in the 100 parts, by weight ; or in volume 21 to 

 79. The properties of these are modified by watery vapor and car- 

 bonic acid gas. The latter is discharged from active volcanoes, mine- 

 ral springs, andthe combustion and decay of organic matter. It is 

 detected in most parts of the atmosphere, and it performs a very im- 

 portant part of the process of vegetable nutrition. The annual evo- 

 lution of carbon from springs and fissures in the volcanic district of 

 the Eifel, has been estimated at 100,000 tons, containing 27,000 tons 

 of carbon. 



The final products of all vegetables are carbonic acid, water and am- 

 monia, which last is a compound of nitrogen and hydrogen. Ammo- 

 nia is supposed to be always present in the air, and is brought down 

 by rain with other matter, as it is always found in rain water. Plants 



