S84 



STARCHES OF CONVOLVULACE^. 



the grain, which becomes broken by irregular transverse and diagonal fissures. As the grain con- 

 tinues to swell, the iiuier portion is converted into a homogeneous, granular mass that collects at 

 the distal end. The more resistant parts of the grain are formed into a thick marginal ring which 

 is finely striated and shows 2 or 3 very distinct, alternate light and dark, concentric rings. These 

 rings become thinner and clearer, and the grain becomes invaginated at the base and a large and 

 shapeless mass is thus formed. 



STARCHES OF CONVOLVULACE^. 



Class, Dicotyledones. Order, Polemoniales. Family, Convolvulacese . Genus 



represented, Batatas. 



The Convolvulacece are closely allied to Solanacece, and include about 30 genera and 800 species 

 of herbs and shrubs, chiefly of a twining or trailing character, which are natives of temperate and 

 tropical regions of both the Old and New Worlds. Some are used as medicines, some as foods, some 

 as garden plants, etc. 



GENUS BATATAS. 



The genus Batatas is by some authors included in the larger genus Ipomcea. It comprises 

 about 20 species, mostly natives of tropical America. Starch was prepared from B. edulis Chois. 

 {IniTponKBa batatas Poir.), which has been cultivated and naturalized in various countries and whose 

 origin remains unkno^^^i. The tuberous roots, like those of Solanum tuberosum, are rich in starch, 

 but contain much more sugar. 



STARCH OF BATATAS EDULIS. (Plate 100, figs. 597 and 598. Chart 390.) 



Histological Characteristics. In form the grains are simple, and seldom occur in aggregates. 

 Nearly all have pressure facets, and the facets are sharply defined and rarely number more than three 

 on a smgle grain, generally only one or two. The conspicuous forms are the dome-shaped to hemi- 

 spherical; quadrangular, spherical with or without one 

 small facet, polygonal with three or more facets, very 

 rarely ovoid, or oval, and various indefinite forms. From 

 the top the grain appears to be spherical. 



The hilum is a distinct, fairly large, round, non- 

 refractive spot, eccentrically placed, even in the spherical 

 grains. It is in or slightly to one side of the median line 

 and may be marked by a small transverse fissure, usually 

 with small branches extending from it. The hilum is 

 never double or multiple. 



The lamella; are quite distinct and follow the outline 

 of the margin, even those near the hilum. They are com- 

 paratively fine, one or two being especially large and dis- 

 tinct. On the larger grains they vary in number from 

 14 to 28. 



The grains vary in size from 3 to 26/f. The com- 

 mon size is about IQjjl. 



Polariscopic Properties. The figure is eccentric and 

 distinct. Four straight lines are seen, of much the same 

 size, sometimes becommg broader at the margin of the grain; at the facets they may become very 

 broad, or appear to widen and to merge into one another, which is probably due to the existence 

 of a depression here. 



The degree of polarization is fairly high. It varies with the position and size of the grain and 

 in the same aspect of a given grain. It is apt to be absent at the facets. 



With selenite the quadrants are well defined, usually irregular in shape, and unequal in size. 

 The colors are fairly pure. The red dividing lines are broad. 



Chart No. 390. 



GV S T CI CA PA FC P S CLP* CA 



MINUTES 

 Curve of Reaction-Intensities of Starch of Batatas edulis. 



