122 BIOLOGY OF PLANTS. 



taneously, an accident which frequently occurs when cotton or 

 wool in large quantities is moistened with them. The princi- 

 pal fixed oils, are olive, croton, palm, cocoanut and linseed oils. 



3. Voldtile oils give a peculiar flavor to plants, called aromatic. 

 They are obtained by distillation of leaves, or by expressing 

 them from the rinds of certain fruits, such as orange, lemon, hur- 

 gamot, etc. Like the fixed oils, they burn with a clear, white 

 flame. The principal volatile oils, are oil of turpentine, lemon, 

 anise, juniper, camomile, caraway, lavender, peppermint, rose- 

 mary, camphor, cinnamon, cloves, sassafras, mustard and bitter 

 almonds. 



4. Resins are the juices of plants, such as exude from pines 

 and balsams; they are generally solid, brittle, and without taste. 

 The resins are well known, under the names of rosin, copal, 

 shell-lac, mastic, dragon's blood, guaiacum, etc. The uses of 

 these are well known. Copal is the basis of all varnishes. 



5. Gum-resins are the hardened juices of several species of 

 plants, which, when cut, give out a milky juice, more or less 

 thick ; these are numerous, and many of them are valuable 

 medicines. Among them are aloes, asafcEtida, ammoniac, gal- 

 banum, gamboge, myrrh, olibanutn, opium, etc. 



Aloes are obtained from several species of trees, especially 

 the aloe vulgaris, from the leaves of which it exudes when cut 

 It is of a reddish-brown color, and of an intensely bitter taste. 



Ammoniac is obtained from the dorema ammoniacum, and is 

 used in medicine, but is the least powerful of all the fcetid gums. 



Asafcetida is obtained from ferula asafatida, a naiive of Per- 

 sia ; it exudes fi-om the roots when cut, in the form of a milky 

 juice. Its taste is acrid and bitter ; its smell strongly alliaceous 

 and foetid. It is employed in medicine, especially in cases of 

 hysteria, asthma and hooping-cough. 



Galhanum is obtained from the plant Galbanum officinale, a 

 native of Persia ; its taste is acrid and bitter, and its smell pe- 

 culiar. It is used in njcdicine for similar purposes with am- 

 moniac, but acts widi less energy than asafcetida. 



Gamboge is obtained from a tree of Siam, and also of Ceylon ; 

 but the s{)ecies is doubtful. It is sold in commerce, under 

 three forms, pipe, cake and lump gamboge. It is employed in 

 water-colored painting, forming a i)urc and fine yellow. It is 

 also used in medicine as a cathartic. 



Myrrh is obtained from the balsamadendron myrrha ; a tree 

 which grows in Arabia and Abyssinia. It exudes from the 

 tree in the state of a yellowish-white liquid, which soon liar- 



