308 PHYSIOLOGY OF NUTRITION. 



observed, however, that fats are not the only substances stained 

 by alkanna tincture and Osmic acid. 



122. The Behaviour of Fats in the Germination of Seeds. 



Very many seeds (Ricinus, Helianthus, Cucurbita, Brassica, 

 etc.) contain fat as non-nitrogenous reserve material. This fat is 

 physiologically equivalent to the starch of starchy seeds. It 

 furnishes the material for respiration, and likewise the material 

 for the formation of the cell-walls. In many cases, however {e.g. 

 Eicinus, Cucurbita), before reaching the place of employment, it is 

 first converted into starch and sugar. In other cases, e.g. in Linum, 

 this can hardly be observed at all, and then the fat must travel 

 in the seedlings mainly as such, in order to render possible the 

 translocation of non-nitrogenous plastic material. In fact, such a 

 migration of fat from cell to cell has been observed by H. Schmidt. 

 We will here follow closely the changes which take place during" 

 the germination of a fatty seed, where this is associated with the 

 formation of large quantities of carbohydrate. 



We select for examination seeds of Ricinus communis. The 

 embryo occupies a central cavity in the copiously developed endo- 

 sperm, and consists of an axis bearing two thin cotyledons. The 

 large cells of the endosperm contain, as we have already deter- 

 mined in another connection, a matrix rich in fat and proteids, in 

 which lie the aleurone grains. Starch is not present in the cells 

 of the endosperm, or in those of the embryo, as we can readily 

 determine by means of Iodine reagents. A few Ricinus seeds are 

 germinated in garden earth in a flower-pot, in the dark, and at a not 

 too low temperature (about 20 C.). When the main root and the 

 hypocotyl have elongated considerably, the upper part of the latter 

 organ being, however, still curved owing to the fact that the 

 cotyledons are still embedded in the endosperm, the cells of the 

 endosperm, as before germination, contain no starch, but only 

 proteid and fat. The function of the cotyledons is to absorb the 

 reserve materials from the endosperm, so that they can be made 

 use of by the young seedling. Much fat is present in the cells of 

 the parenchyma of the cotyledons ; starch, which, as mentioned, 

 was completely absent from the cotyledonary tissue before the 

 commencement of germination, is found abundantly in those 

 parenchyma cells which surround the midribs on the outside. 

 The cambium cells of the hypecotyl contain only proteid material. 



