882 



STABCHES OF SOLANACE^. 



STARCHES OF SOLANACE^. 



Class, Dicotyledones. Order, Polemoniales. Family, Solanaceae. 



represented, Solanum. 



Genus 



Chart No. 389. 



The Solanacew include about 72 genera and 1,500 species, among which are a large number of 

 well-known plants, of importance as sources of medicines, foods, condiments, etc. They are widely 

 distributed in the warm climates of both hemispheres. 



GENUS SOLANUM. 



The enormous genus Solanum includes, according to published accounts, about 950 species, 

 about three-fourths of which are distinct. About 15 species are natives of the United States. Starch 

 was prepared from the tubers of S. tuberosum Linn., which were bought in the open market, and 

 therefore of some horticultural form. This species, the common potato and so-called Irish potato, 

 is a native of the Andes of Chili and Peru, from which regions it has been distributed over the civil- 

 ized world. In the wild state the tubers are small, but by cultivation they have been increased to 

 fifteen to thirty times the natural bulk. They are rich in starch, which is used in the manufacture 

 of dextrin, sugar, and alcohol, and for laundering and other economic purposes, and it has at times 

 been marketed as an arrowroot. (See Marantacece, page 813.) The consumption of the tubers as a 

 food, as is well-known, is enormous. 



STARCH OF SOLANUM TUBEROSUM. (Plate 100, figs. 695 and 596. Chart 389.) 



Histological Characteristics. — In form the grains are usually simple. There are a few compound 

 grains which consist of two or three components; and there are aggregates, especially among the 

 smaller grains, which consist of from two to four components. There are pressure facets on a few 

 grains, sometimes one or two. There is no tendency to occur in clumps. The surface of the grains 

 is rounded and quite smooth and irregularities of the margin are quite slight. The conspicuous 

 forms are ovoid, flattened ovoid, oval, and round; also 

 pyriform, rarely triangular with rounded angles, and 

 dome-shaped to hemispherical. Some of the larger grains 

 are slightly flattened. 



The hilum is a distinct, small, usually round, non- 

 refractive spot. Rarely it is elliptical or lenticular. It is 

 usually at the larger end of the grain, but often very 

 much to one side of the longitudinal line. The hilum is 

 sometimes marked by a small fissure which may be trans- 

 verse, diagonal, longitudinal, and 3- or 4-armed. Double 

 hila are not uncommon, and even 3 and 4 hila may be 

 seen in a single grain. These may be grouped closely or be 

 far apart, and they are usually separated by slight fissures. 



The lamelUje are distinct, fine, and, as a rule, regular 

 in outline and tend to follow the outline of the margin. 

 The lamellae average from 27 to 42 on medium-sized and 

 large grains. 



The grains vary m size from 15 to 70/x. The common 

 size is 44ju. 



Polariscojnc Properties. — The figure is eccentric and 

 distinct. All four of the lines are seen in part or in whole, one or two being much longer than the 

 others. The lines are usually fairly clear-cut; they vary in width and are l^roader near the margin. 

 Double figures are occasionally noted. 



The degree of -polarization is very high. Some of the larger grains sliow polarization colors. 

 Polarization is as high in this starch as in any of the starches examined, with the possible exception 

 of the cannas. It varies somewhat in different grains, in different positions of the same grain, 

 and sometimes in different parts of the same aspect of a given grain. 



PS C) PA CA 

 "^ PC PS 



Curve of Reaction-Intensities of Starch of Solanum 

 tuberosum. 



