1 6^ THE PLANT WORLD. 



Citric acid makes lemons and currants sour. Lime juice from Citrus 

 Ihnelta is a useful medicine for the prevention of scurvy, and is used 

 for this purpose in the British navy. In Montserrat, there are 600 

 acres bearing 120,000 of these trees. Only the fruit that falls to the 

 ground is used, it being collected every morning. The acid is found 

 in the pulp. From the rind, as from oranges and lemons, an oil is 

 extracted. 



Fats or oils are found in many plants in cells, or glands, or special 

 canals like the vittae, oil canals of fruits of Umbellifera;. They are 

 free, or mixed with stearin, palmatin, olein and albuminoids, and are 

 products of assimilation. 'Fluid oils are fixed or volatile, the fixed 

 being characterized as non-drying and drying. The non-drying are 

 charged with olein, and leave a grease spot on paper or cloth. Drying 

 oils contain linolein. At ordinary temperature, they are fluid. The 

 most viscid is castor oil, two hundred times as thick as water. Olive, 

 linseed and flaxseed oils are from ten to twenty times as thick. 



Etherial oils make the fragrance of oranges, mints, bergamonts, 

 mustard, myrrh, sassafras, wintergreen, etc., found in special glands. 

 The dotted appearance of the leaves of such plants as the St. John's- 

 wort and myrtle, is due to the presence of numerous cavities or cells, 

 containing essential oils. They dissolve in waterwith difficulty, but 

 readily in alcohol, ether and the fatty oils. They leave no permanent 

 grease spot on paper. 



Gums are amorphous substances, which, when they do not dis- 

 solve in water, form thick, viscous masses in it. Pure gum is soluble 

 in water, insoluble in 60?; alcohol or ether. Pectose, a neutral, in- 

 soluble body, found in some fleshy roots, as carrots and beets, also in 

 some under-ripe fruits, as in the juice of apples, pears and quinces, 

 when combined with sugar, makes our fruit jellies. Housewives 

 know that fruit picked late in the season, too ripe, will not make jelly. 



Resins are mixtures of gums with volatile oils. They are fluid 

 balsams. 



Balsams are intermediate between volatile oils and pure resins. 



The alkaloids found in some of our plants, form virulent vegetable 

 poisons, and are useful in small quantities in pharmacy. Morphia is 

 an example. They will sometimes kill the plant from which they are 

 derived. Morphia kills the poppy. 



Ferments are found in plant juices. The papaw tree is full of 

 milky juice, and on account of the ferment which it contains, old and 

 tough meat is made tender by wrapping it a few hours in the leaves 

 of that tree. 



By far the greater number of plants, whose juice is of value, grow 

 in the tropics. Great heat induces greater activity of the plant forces 



