SECRETIONS 283 



On account of the hydrocyanic acid or other poisonous substances 

 contained, many of the glucosides are poisonous. For example, 

 the saponins, which are present in Corn Cockle and Cow Cockle, 

 are poisonous and make the seeds of these plants very objection- 

 able impurities of the small grains. The mustards, a number 

 of which have poisonous seeds, contain sinigrin, a poisonous 

 glucoside. In the seeds of some Beans, as the Burma Bean, there 

 is phaseolunatin, a poisonous glucoside. 



Although it is not known just how glucosides are formed or 

 their exact function to the plant, their structure shows that the 

 photosynthetic sugar furnishes most of the elements. Some 

 of them may be directly synthesized, while others may result 

 from the decomposition of more complex compounds. For the 

 decomposition of each kind of glucoside there seems to be a special 

 enzyme. 



The alkaloids constitute another group of substances whose 

 origin and function are obscure. Some of the familiar ones are 

 caffein and thein in Coffee and Tea, nicotine in Tobacco, morphine 

 from the Poppy, quinine from the bark of the Cinchona tree, and 

 strychnine from the seeds of Nux vomica. In containing C, H, O, N, 

 they show a close relationship to the amino-compounds. The 

 alkaloids are probably protective substances, since they are 

 often unpleasant to the taste and the most poisonous group of 

 the plant substances. In the preparation of drugs, the alkaloids 

 have a very important place. They are the plant poisons which 

 commonly poison stock in pastures and often people get them 

 by mistake. In Poison Hemlock (Conium maculatum) and 

 Water Hemlock (Cicuta maculata) there is the poisonous alkaloid, 

 known as conin, which is poisonous to stock and man. In the 

 Nightshade family, of which Tomatoes and Irish Potatoes are 

 representatives, there are a number of plants which contain 

 atropine and solanin, which are poisonous alkaloids. There is 

 a large number of plants, many of which are common, that are 

 poisonous on account of the alkaloids contained. The ptomaines, 

 the poisonous substances which Bacteria produce in the decom- 

 position of meats, are alkaloids. 



Pigments are the substances upon which the colors in plants 

 depend. Their origin is obscure and in some cases their function 

 is not known. The one most prominent is chlorophyll with the 

 formula often given as C5 5 H7 2 O 6 N4Mg. Associated with chloro- 



