102 SECRETION. 



In some parts of America, where tallow is scarce, the 

 wax is annually collected from the Myrica cerifera, and 

 made into candles. In the Ceroxylon andicola of 

 Humboldt and Bonpland, it is secreted in abundance on 

 the foliage, and what is called the bloom of many fruits 

 and flowers is a sort of waxy exudation. 



120. Oil, as a product of vegetable bodies, is of two 

 kinds, fixed and volatile ; the former require a tempera- 

 ture of 600 to decompose them, and are little affected 

 by water and alcohol, the latter rise in vapour at 300, 

 and are soluble in alcohol. 



121. The fixed oils are found in the cells of the 

 tissue of a great many seeds, as the Walnut, hemp, 

 castor oil, etc. In the ripe state, these seeds, according 

 to Meyen, show no trace of fecula, but which is visible 

 enough during the first period of the evolution of the 

 embryo, and therefore we may conclude, that it has 

 been converted to the fixed oil we find at an after 

 period. In germination, this oil is converted into a 

 saccharine mucilage, which nourishes the developing 

 plant like the sugar in other cases ; and, therefore, fixed 

 oil may be looked upon, along with starch, gum, and 

 sugar, as belonging to the nourishment of plants. 



122. Though the seed and its coverings are the places 

 in which fixed oil is mostly found, it is met with in other 

 situations as well, and is found swimming in a fluid 

 contained within cells, as in some Charas. 



The following seeds in 100 parts of their weight, con- 

 tain a proportion of oil as below : 



Hazel-nut 60 Brassica napus Ol 83 



Garden-cress , . . 56 58 Brass, preecox 30 



Olive 5.0 Reseda luteola 30 



Walnut 50 Hemp 25 



Poppy 47 50 Flax 24 



Almond 46 Pinus sylvestris 22 



Euphorbia lathyris .... 41 Sunflower 15 



Brassica campestris Ol. . 39 Grape-seeds 10 11 



123. Volatile Oils are generally distributed over most 

 portions of plants, being deposited pure in leaves, flowers, 



