THE KINDS OF STORED FOOD 



179 



ordinary temperatures, and olein is fluid, and whether the mix- 

 tures of these be fluid or solid depends upon their relative 

 proportions. 



The fatty oils occur in greatest abundance in oily fruits and 

 seeds, as in the fruit of the olive, and the seeds of castor bean, 

 where 60 per cent, of the dry weight is oil, and in rape seed, 

 with 50 per cent, of rape oil, and in walnuts, with 55 per cent, 

 of walnut oil in the embryos. There are many seeds not classi- 

 fied as oily which nevertheless contain enough oil to make them 

 the source of its commercial production; some of the cereals 

 are an example of this, and notably Zea mais. 



In reviewing all groups of seed plants it has been estimated 

 that four-fifths of them contain fats and oils as an important 

 part of the non-nitrogenous reserve food in the seeds. 



The fats and oils in seeds are reserve food to be used during 

 germination, but when they occur in fruits, as in the olive, they 

 are not food for the em- 

 bryo, but are useful in 

 alluring animals to gather 

 the fruit and scatter the 

 seeds. 



Tnulm. — Inulin is a car- 

 bohydrate occurring nota- 

 bly in the underground 

 parts of some Compositae, 

 such as Taraxacum and 

 Dahlia, and it also occurs in the Campanulaceae, Lobeliaceae, 

 Liliaceae, and Amaryllidaceae, and a few other families. 



Inulin is soluble in the cell-sap, and on freezing, or when 

 placed in alcohol or glycerine, it is precipitated in the form of 

 sphaerocrystals (Fig. 98). It is apparently made from dextrose 

 and laevulose, and it is changed back into these or other sugars 

 preparatory to its circulation. 



Reserve Cellulose and Amyloid. — Reserve cellulose is de- 

 posited in the form of thickenings of the cell-wall in the endo- 

 sperm of the date and other palms, and in species of Foeniculum. 



Fig. 98. — Sphaero-crystals of inulin from tuber 

 of Dahlia variabilis. A, precipitated from an 

 aqueous solution; B, precipitated within the cells 

 by long standing in alcohol. (After Sachs.) 



