886 



STARCHES OP GESNERACE^. 



STARCHES OF GESNERACE/E. 



Class, Dicotyledones . Order, Polemoniales . Family, Gcsneraceae. 

 represented : Gesneria and Gloxinia (Sinningia) . 



Genera 



The Gesneracece include about 70 genera and 700 species of herbs and shrubs, natives of tropical 

 and semitropical regions, chiefly of America. They are cultivated chiefly for their flowers. The 

 fruits of some are used as a food. 



GENUS GESNERIA. 



This genus comprises alout 50 species of tuberous, bulbous, or rhizomatous herbs, natives of 

 South America, chiefly of Brazil. Starch was prepared from G. luhijlora Hort. 



STARCH OF GESNERIA TUBIFLORA. (Plate 100, figs. 599 and 600. Chart 391.) 



Histological Characteristics. In form the grains are simple; there are no aggregates or pressure 

 facets, and only a few small clumps. The surface of the grain is generally irregular, owing in part 

 to secondary deposits of starch, made after the original grain has been formed and other such irreg- 

 ularities of development, and in part to nipple-like processes. The additions are lamcllated and 

 usually at the sides or near the base of the grain. Often the lamella composing them may be seen 

 to be continuous around the grain. A small hollow frequently extends into the substance of the 

 grain from the distal end, which is usually squared. The conspicuous forms are the flattened ellip- 

 soidal, which is usually straight but may be bent on the 

 long or longitudinal axis. The proximal end is rounded 

 and commonly larger than the distal end. There are also 

 ovoid, pj^riform, round and also triangular, club, gourd, 

 and boot shapes, and various indefinite forms which arise 

 from causes noted. The grains are not flattened, but 

 owing to the secondary deposits they are sometimes 

 broader than thick. They bear certain general and 

 striking resemblances to the starches of Dicffenbachia. 



The hilum is a not very distinct, small, non-refrac- 

 tive spot, situated usually very eccentrically at the larger 

 or proximal end of the grain. It is commonly in or near 

 the median line. There are neither double nor multiple 

 hila. It is rarely fissured, and if so the fissure is a very 

 small transverse line. In the grains with secondary ad- 

 ditions, the hilum is always in the primary part of the 

 grain, but it may be very much to one side of the 

 longitudinal axis. 



The lanielloe are distinct and comparatively fine. 

 Those near the distal end are the coarser, but not always 

 the more distinct. In the grains with secondary lamella) the lamella? of the original grain are 

 usually the more distinct. The lamellse are regular, and excepting the circles around the hilum 

 are in the form of arcs of circles having the form of the distal margin. They vary in distinctness in 

 different grains. There are from 35 to 40 on the larger grains. 



The grains vary in size from 6 to 46ai. The common dimensions of the largest ellipsoidal grains 

 are 44 by 14/u in length and breadth. The common size is 22/Lt. 



Polariscopic Properties. The figure is very eccentric, distinct, and clear-cut. It exliibits many 

 peculiarities, some being due to the secondary additions before noted, in which cases the lines, in- 

 stead of ending at the margin of the primary part of the grain, may curve aroimd the margin and 

 are bent so as to extend down to the secondary additions, where they end. They are usually quite 

 sharply defined and may be straight or curved, and a given line may be of equal or unequal width 

 in its course. 



The degree of polarization is fairly high. It varies in different grains, in different aspects of 

 the same grain, and in parts of the same aspect of a grain. 



Curve of Reaction-Intensities of Starch of Gesneria 

 tubiflora. 



