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 stnigrin, 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 CssH,2OsN,sMg. Associated with chloro- 
