36 FATS, OILS, AND WAXES 



metres required for neutralization multiplied by 5*61 and 

 divided by the weight of fat taken gives the acetyl value. 



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. 



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, Ornithogalum, etc., in the flower of a Dicoty- 

 ledon, Gaillardia Lorenziana, and in Psilotum. 



The development of the elaioplasts of Gaillardia has been 

 followed by Beer,* who found that they are formed by the 

 aggregation of chloroplasts which then degenerate and give 

 origin to the oil. He considers it is most unlikely that elai'o- 

 plasts perform any function of direct importance to the life of 

 the plant, although they may in some cases, the corolla-hairs 

 of Gaillardia, for instance, serve a biological purpose. 



But although elaioplasts may not perform the function 

 originally ascribed to them, it does not necessarily follow that 

 fats, more especially when occurring in the green parts of 

 plants, may not be direct photosynthetic products. Thus 

 Fleissig considers that in the case of Vaucheria, a plant which 

 contains an abundance of fat, this substance is a direct photo- 

 synthetic product comparable to the starch and sugar in 

 ordinary green leaves. On the other hand, it is, of course, 

 possible that the fats in such cases may have been produced by 

 secondary changes in the original product of photosynthesis. 



In many cases there can be but little doubt that fats are 



* Beer : " Ann, Bot.," 1909, 23, 63. 



