136 



PART II. — VEGETABLE HISTOLOGY. 



Well developed starch grains are observed to possess a 

 nucleus or hilum, around which the rest of the granule is 

 arranged in layers. These layers differ from each other some- 

 what in transparency, owing to the fact that some of them con- 

 tain more water than others. This structure gives rise to the 

 appearance of delicate markings, which, in case the nucleus is 

 centrally located, as in the starch of the Bean, Fig. 382, are con- 

 centric, but if near one end, as in Potato and Curcuma starch, 

 are eccentric. Starch grains are composed of two somewhat 

 different substances, granulose, which forms the larger proportion 

 of the weight of the grain, and starch-cellulose. 



Inulin is a body which, chemically, is closely related to starch 

 and isomeric with it. It takes the place of that substance in 

 many members of the natural order Compositae. It is abundant, 

 for example, in the roots of Elacampane, Dandelion, Chicory, 

 Dahlia, and the Artichoke. It is 

 also occasionally found in members 

 of other natural orders. It occurs 

 in solution in the cell-sap, but if 

 parts containing it be soaked for a 

 time in strong alcohol, and sections 

 of them be examined microscop- 

 ically, sphere-crystals of it will be 

 observed in the cells, as shown in 



Fig. 3&3- 



blue, as it does starch, but, like starch, it is converted into 



glucose by the action of dilute sulphuric acid. 



Among the other carbohydrates found in solution in the cell 

 sap are dextrin (C 6 H, 2 O s ), somewhat intermediate in its char- 

 acter between starch and sugar ; mucilage and gum, both closely 

 related to starch, and in some cases, at least, derived from it, 

 and the sugars, including glucose (C 6 H,.j0 6 ), cane sugar (Ci 2 H 22 

 On), and various other sugars. 



Vegetable Acids. Among the more important of these 

 may be mentioned malic acid (C 4 H 6 6 ), a very common acid 

 in fruits, but also found in other parts of plants; oxalic acid 

 (H 2 C 2 4 ), an abundant and widely distributed vegetable acid ; 

 citric acid (C 6 H 8 T ), that which communicates the acidulous 

 taste to lemons, limes, and other fruits of the Orange family of 



Fig. 379. — Maranta starch. 

 Iodine does not Stain it nified about 27s diameters. 



Max- 



