GENUS TIGRIDIA. 



713 



gelatinized except that immediately surrounding the hilum or the fissures at the hilum. These 

 fissures now begin to grow wider and separate the starch here into several pieces which gelatinize 

 independently of one another. The resulting gelatinized grain is very large, and the capsule is usually 

 much twisted, sacculated, and otherwise distorted. 



The reaction with Piirdifs solution begins in some grains in 40 seconds. About four-fifths are 

 partially gelatinized in 5 minutes and all are completely gelatinized in 25 minutes. The reaction 

 begins by the breaking up of the starch between the hilum and the distal end into granules, which 

 granules gradually pass into a gelatinous mass, leaving a very thin capsule except at the proximal 

 end, where there is a thick, striated strip of starch which finally becomes thin and transparent. 

 The gelatinized grain is large and the capsule is somewhat folded and sacculated, but not so much 

 so as is the case in the reaction with pyrogallic acid. 



STARCH OF TIGRIDIA PAVONIA VAR. CONCHIFLORA. (Plate 68, figa. 405 and 406. Chart 271.) 



Histological Characteristics. In form the grains are simple. There are a few aggregates and 

 clumps. No pressure facets were observed on the grains. The surface of the grains is generally 

 somewhat irregular, owing to variations in the development of parts of the margin, sometimes in 

 the form of nodular or nipple-like protrusions. Depres- 

 sions of the margin at each side of the hilum, giving the 

 proximal end the appearance of a protuberance, are not 

 rare. The small grains are numerous and of various 

 shapes, chiefly rounded, elliptical, and polygonal. The 

 conspicuous forms are the lima-bean-shaped, reniform, 

 oval, and ovoid. There are also spindle-shaped grains, 

 some having the longitudinal axis shorter than the trans- 

 verse axis; also some irregularly shaped grains of various 

 forms. The grains are somewhat flattened and about 

 one-third to one-half as thick as they are broad. 



The hihnn is usually fissured, and when not it ap- 

 pears as a distinct, comparatively large round spot. It 

 is eccentric from a degree varying from very slight to 

 one-third, usually two-fifths, of the longitudinal axis. 

 The fissure usually takes the form of three or four nar- 

 row but rather irregular lines radiating from a common 

 center or from a straight transverse line. Stellate or 

 variable arrangements of irregular fissures also occur. 



The lamellce are not distinct, fine, regular arcs of 

 circles, or continuous ellipses about the hilum, or bands of the same shape as the outline of the grain. 

 Those near the hilum are not so fine but more distinct than those near the margin of the grain. The 

 number could not be accurately determined. 



The grains vary in size from 8 by 8^ to 26 by Mn in length and breadth. The common size is 

 20 by 24/u in length and breadth. 



Polariscopic Properties. The figure is eccentric and usually very obscure. A large area of 

 the central part of the grain in some cases, practically the whole of the grain, is dark. In a few 

 grains (probably grains on edge or end) the figm-e is fairly clear-cut and the lines fairly regular. 



The degree of polarization extends from very low to fair, varying much in different aspects of 

 the same grain, and is from fair to high when the grain is viewed on end or edge. In the broad 

 aspect of a grain polarization is often absent in a central area of variable size, sometimes about as 

 large as the grain. It is lower, on the whole, than that of T. pavonia var. grandiflora alba. 



With selenite the quadrants are generally not defined and are very irregular in form and unequal 

 in size. The colors are not pure. 



Iodine Reactions. With 0.25 per cent Lugol's solution the grains all color a fairly deep indigo; 

 with 0.125 per cent solution they color fairly, the color deepens gradually, and is deeper than that 

 of the grains of T. pavonia var. grandiflora alba. After heating in water until the grains are com- 

 pletely gelatinized, the solution colors fairly and the gelatinized grains deeply on the addition of 

 iodine. After boiling for 2 minutes the solution colors very deeply, but the grain-residues lightly. 

 The capsules all color a pale violet with an excess of iodine. 



Curve of Reaction-Intensities of Starch of Tigridia 

 pavonia var. conchiflora. 



