34 FATS, OILS, AND WAXES 



Hardening of Oils.— Many low-melting fats or oils are 

 nowadays hardened by treating them with hydrogen in the 

 presence of a nickel catalyst ; the process of hydrogenation 

 involves the removal of the double bonds of saturation with 

 hydrogen, the resulting saturated compound having a higher 

 melting-point. 



PHYSIOLOGICAL SIGNIFICANCE OF FATS. 



The great function of fats in the economy of the plant is 

 connected with nutrition. They form one of the most im- 

 portant food-reserves of plants and as such may occur in 

 vegetative or in propagative organs. 



It is, however, not possible to ascribe this function to all 

 instances of fat occurrence. Thus, in the case of the palm 

 Elaeis guineensis, two distinct types of fat occur ; the one in 

 the pericarp, the palm oil of commerce, and the other in the 

 testa adjacent to the embryo. Apart from the fact that these 

 two fats are different, the former being of the nature of 

 tallow and containing palmitic, stearic, and other fatty acids, 

 and the latter containing acids of a lower molecular weight, 

 it is difficult to see what nutritive purpose a fat occurring in 

 the pericarp can serve in view of the fact that it is destroyed 

 before germination actually begins ; it has, moreover, been 

 shown that germination is hastened if the pericarp is removed 

 prior to planting. Similar considerations also apply in the 

 case of the olive. 



With regard to their origin in plants very little is known ; 

 they first appear as very small vacuoles in the protoplasm 

 which eventually run together forming large drops. 



In some cases oil has been described as owing its origin 

 to the activity of elaioplasts, which are colourless bodies of 

 various shapes usually grouped around the nucleus, and, like 

 other plastids, of a protoplasmic nature. They are, or have 

 been, supposed to act with regard to oil formation much as 

 leucoplasts do with respect to starch formation. Elaioplasts 

 have been observed in many Monocotyledons such as Vanilla, 

 Funkia, Gagea, OrniOiogalum, etc., in the ffower of a Dicoty- 

 ledon, Gaillardia Lorenziana, and in Psilotum. 



