INULIN. FATS. PROTEINS 415 



The best known of the remaining soluble reserve carbohydrates is 

 inulin, 195 which is so characteristic a chemical component in the 

 Compositae ; ill the root-tubers of Dahlia variabilis, in llelianihus 

 annuus and in Inula Helenium, this substance occurs in the form of a 

 highly concentrated solution presenting the appearance of a mobile, 

 pale yellow oil. When a freshly-prepared section of an inulin - 

 containing tuber is treated with alcohol, the polysaccharide is thrown 

 down as a finely granular precipitate. But if a whole tuber is kept 

 in spirit for a long time, the slow entrance of the alcohol permits of 

 the formation of large sphaerocrystals of inulin, which are usually 

 aggregated into groups ; when precipitated in this way, individual 

 sphaerites often extend over a number of cells. Other carbohydrates 

 which resemble inulin in their chemical relation to fructose (triticin, 

 graminin, scillin, irisin), occur in various Monocotyledons. 



The fatty substances which serve as reserve-materials, belong, like 

 vegetable fats in general, to the class of glycerides ; they are, in fact, 

 glycerine-esters of various fatty acids (especially of palmitic, stearic 

 and oleic acids). The majority of fats are liquid at ordinary tempera- 

 tures (fatty oils) ; less frequently they are of the consistency of tallow 

 or butter {e.g. cacao-butter and nutmeg-fat). They are readily soluble 

 in ether, carbon disulphide and benzole ; castor-oil is completely 

 soluble in alcohol, even in the cold. In their natural condition the 

 vegetable fats are never chemically pure substances ; frequently they 

 are accompanied by free fatty acids, and sometimes also by pigments 

 (palm-oil), or by cholesterine (olive-oil and almond-oil). 



When the amount of fat in a storage-cell is not very large, it is 

 usually suspended in the protoplasm in the form of minute droplets 

 or vesicles. In oily seeds, on the contrary, only a small quantity of 

 the fat is present in this finely divided state ; the greater proportion 

 is contained in the interstices between the delicate meshwork of the 

 cytoplasm on the one hand, and the so-called aleurone grains (see 

 below, p. 417) on the other. 



2. Nitrogenous reserve-materials. Nitrogenous materials are almost 

 always stored either in the form of proteins or of amides [and amino- 

 acids]. 194 In the latter category are comprised asparagin the most 

 important of the vegetable amides further, glutamin, leucin, tyrosin, 

 etc. The reserve proteins include the various globulins, vitellins [phyto- 

 vitellins] and albumoses, also certain nucleoproteids, and the members 

 of the gluten group. 



In succulent storage-organs such as the majority of tubers, bulbs 

 and rhizomes the nitrogenous reserve-materials are for the most part 

 dissolved in the cell-sap. 195 Thus, if a fairly thick section, taken from a 

 mature potato tuber, is treated with alcohol, a bulky and somewhat 



