888 



STARCHES OF GESNERACE^. 



The grains are often irregular, which is 

 Chart No. 392. 



to enlarge, the enlargement taking place particularly upward. The distal end in the meantime 

 becomes gelatinous with much irregular swelling and lobulation, the central part finally reacting. 

 The other type of process begins at the distal end, followed by reaction at the hilum, after which 

 the changes are similar to that of the first type. The gelatinized grains so formed are very large, 

 thin-walled, and transparent. They are very much distorted, lobulated, and infolded, and bear 

 but little resemblance to the original grain. 



With Purdy's solution there is a slight general reaction in a minute. A very few grains are 

 completely gelatinized in 15 minutes, about half in an hour, and nearly all except the smaller grains 

 are gelatinized in 2}^ hours. The hilum and lamella are both very prominent. The reaction is 

 similar to that with pyrogallic acid, but there seems to be a form of starch about the depression at 

 the distal end of the grain which is especially resistant to this reagent. 



GENUS GLOXINIA (SINNINGIA). 



The garden gloxinias belong to the genus Sinningia (which includes Rosanowia) and are forms 

 of the Sinningia spedosa type. The genus comprises about 16 species, all of which are Brazilian. 

 The starch studied in this investigation was obtained from an unnamed garden variety, and in 

 accordance with usage is referred to as a Gloxinia. Gesneria and Gloxinia {Sinningia) have been 

 hybridized. 



STARCH OF GLOXINIA VAR. (Plate 101, figs. 601 and 602. Chart 392.) 



Histological Characteristics. In form the grains are almost wholly simple and isolated, except 

 a small number which occur in small aggregates and occasional small clumps. There are a few com- 

 pounds. Some of the isolated grains bear pressure facets, 

 chiefly due to the following causes : to the deposition of a 

 secondary set of lamellse placed at varying angles to the 

 primary lamellae; to the appearance of one or more inden- 

 tations, probably pressure facets of small grains, at differ- 

 ent points on the surface; and, rarely, to the presence of 

 a finger-like or one or two small nipple-like protuberances 

 at or near the proximal end. The conspicuous forms are 

 club-shaped, elongated ovoid with a squared or sharply 

 pointed end, ovoid, ellipsoidal, and triangular with 

 romided angles and either a curved or diagonal base. 

 There are also nearly round, pyriform, somewhat mussel- 

 shell-shaped, knob-shaped, and boot-shaped grains. The 

 grains when seen on end are not flattened, except a few 

 which are broader at the distal end. 



The hilum is usually observed as a clear, romid 

 spot eccentric about one-sixth to one-fourth of the longi- 

 tudinal axis. It is generally not fissured. A curved 

 transverse cleft, or two clefts which intersect and form 

 a cross, may be observed. 



The lamellcB are arranged in groups of numerous fine lamellae interspersed with from two to 

 five which are coarser and more refractive. They are circular or elliptical complete rings near the 

 hilum, but are probably incomplete and follow the outline of the grain when near the distal end. 

 On the large grains 80 to 85 lamellae have been counted and 46 to 50 on the medium-sized ones. 



The grains vary in size; the smaller are 5 by 3/i; the larger are 76 by 28fi in length and breadth; 

 the grains of common size are 30 by IS/x in length and breadth. 



Polariscopic Properties. The figure is eccentric and clean-cut. Its lines are rather narrow and 

 intersect at an oblique angle. They are sometimes straight, but more often bent and occasionally 

 bisected. 



The degree of polarization is high to very high. 



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

 colors are generally pure; there is a greenish tint in a few grains. 



Iodine Reactions. With 0.25 per cent Lugol's solution all the grains color a deep blue-violet, 

 which deepens rapidly; with 0.125 per cent solution they soon color a light blue-violet, which 



Curve of Reaction-Intensities of Starch of Gloxinia var. 



