BOTANY. 39 



I 



atmosphere by means of the leaves. Thus the phmt decomposes carbonic 

 acid, assimilates the carbon, and liberates the oxygen ; an animal, on the 

 other hand, deprives the air of its oxygen, and liberates carbonic acid. 

 Oxygen is next in importance to carbon. It is usually found in combination 

 with hydrogen, forming water. Nitkogen is less an universal constituent 

 than the other, being chiefly found in the younger parts and the seeds. 

 These four elements occur as binary compounds in water and oily matters : 

 as ternary in starch, gum, sugar, and cellulose ; and as quaternary in gluten, 

 caseine, albumen, and fibrine. The latter compounds have for their base a 

 substance known as proteine (0^°, IP', N^ O''^). with the addition of certain 

 proportions of sulphur and phosphorus. 



The principal inorganic constituents of plants are formed of combinations of 

 chlorine, iodine, bromine, sulphur, phosphorus, potassium, sodium, calcium, 

 magnesium, aluminum, silicon, iron, manganese, and copper. 



Silica abounds in grasses, giving firmness to the stem. It is sometimes 

 found aggregated in the joints of the bamboo as tabasheer. Lime is found in 

 all plants, in some existing in large quantity. It occurs as a carbonate on the 

 surface of some plants. Soda and Potash are also of constant occurrence. 

 Plants growing near the sea exhibit a preponderance of soda, while those that 

 are inland abound most in potash. Iron and Manganese are found in small 

 quantity ; Copper has been detected in coflee. 



B. Products and Secretions of Plants. 



Having thus very briefly mentioned the principal elements found in 

 plants, we proceed next to a summary of their most important compounds. 

 The first to be mentioned is starch, Avhicli is stored up to serve as nourish- 

 ment either to the developed plant or to the embryo. Its chemical 

 composition is C"^, 11'°, 0'". Starch may be deposited in seeds, roots, stems, 

 receptacles, &.c. Sometimes starch is associated with poisonous or acrid 

 juices. Inuline is a substance analogous to starch, and found in Elecampane 

 and other plants ; lichenhic, another variety, is found in Cetraria islandica. 

 or Iceland moss. The action of sulphuric acid, or of malt, on starch, or long 

 boiling in water, results in the production of a soluble substance, called 

 dextrine, and is one of the stages through which starch passes to become 

 sugar. 



Gum (C^, H", 0") is another substance found abundantly in the vegetable 

 kingdom, and is one of the forms through which organic matter passes during 

 the growth of plants. There are two forms of gum : one soluble in water (ara- 

 bine or mucilage), the other only swelling up into a gelatinous mass (bassorine. 

 cerasine, and pectine). Arahine is known familiarly as gum arable ; combined 

 Avith cerasine it is found in the gum of the cherry and plum tree. Mucilage 

 is present in many plants, as in the mallows and in linseed. Bassorine forms 

 the chief part of gum tragacanth. Pectine is obtained from pulpy fruits, as 

 the apple and pear. It forms a jelly with water, and when dried resembles 

 isinglass or gelatine. 



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