THE PLANT 95 



(amino-succinamic acid), CO.(NH2).C,H3(NH,).CO.OH, may br 

 taken as typical. This substance, which is both an amide and 

 an amino-acid, is soluble in water, and, like most amides, is 

 crystallisable. It occurs in asparagus, in the young shoots of 

 vetches, beans, peas and many other plants. 



VIII. The Alkaloids. — These substances may be regarded 

 as derived from ammonia, NH,, by the replacement of the 

 whole or part of the hydrogen by complex organic groups. 

 They are usually possessed of powerful medicinal properties, and 

 occur only in certain plants, sometimes in the seed, sometimes 

 in the leaves, and sometimes in other parts of the plant. They 

 are of no value as direct foods, but are often valued in medicine. 



Caffeine or theine, CgHjgN^O^, occurring in tea and cofiee, 

 and theobromine, CyllgN^Oj, found in cocoa, though by some 

 authorities not regarded as true alkaloids, may be mentioned ; 

 while as examples of undoubted alkaloids, quinine {in Peruvian 

 bark), Cj^Hj^NjO,, strychnine (in nux vomica beans), CjjHjjNjOj, 

 morphine (in poppy heads), CjyIIjjNO,, and nicotine (in tobacco 

 leaves), C,^H,oNj, may be cited. 



IX. Chlorophyll, also a nitrogenous body, has been much 

 investigated. It is the green colouring substance present in the 

 leaves and stems of almost all plants, and intimately connected 

 with the assimilation, under the influence of light, of carbon 

 from carbon dioxide. It has the composition represented by 

 the formula, CssH^OgN^Mg, and contains, as its fundamental 

 constituent, chlorophyllin Cg^HgjOeN^Mg. It is easily extracted 

 by alcohol, ether, or carbon disulphide. 



Though iron is essential for its production in the plant, the 

 coloured substance itself is free from iron. Except in this last 

 fact it appears to possess some similarity in composition and 

 constitution to the red colouring substance — haemoglobin — of 

 the blood of animals. Indeed, recent investigations tend to 

 show that the characteristic constituent of chlorophyll and of 

 hsematin (the coloured part of haemoglobin) have the same 

 constitution, except that in chlorophyll, magnesium replaces 

 the iron of haematin. 



