GENERA TIGRIDIA AND GLADIOLUS. 



715 



NOTES ON THE STARCHES OF TIGRIDIA. 



The two varieties of Tigridia pavonia are very nearly alike in all respects, the main differences 

 being in the histological properties in size, in the reactions, in the degree of polarization, and in 

 the temperature of gelatinization. All the differences are within the normal limits of error of ex- 

 periment and observation. 



GENUS GLADIOLUS. 



This genus of iridaceous, cormous or bulbous plants includes about 140 species, mostly natives of 

 Cape Colony and Natal. About 15 species are natives of the Mediterranean region, and a few have 

 been found in the mountains of tropical Africa. Most of the cultivated forms are species or hybrids 

 referable to the South African group and represented chiefly by G. cardinalis, G. florihundus, G. psit- 

 tadnus, and G. blandus. The European group is represented chiefly by G. hyzanlinus and G. com- 

 munis. Starches from 4 species were examined, including G. byzantinus Miller, G. pmnulinus Baker, 

 G. cardinalis var. (Blushing Bride), and G. florihundus Jacq. G. byzantinus is a Mediterranean species; 

 G. primuliyius is from Victoria Falls, South Africa, and according to Baker resembles G. psitlacinus, 

 G. dracocephalus, and G. quartinianus; and both G. cardinalis and G. florihundus are South African. 



STARCH OF GLADIOLUS BYZANTINUS. (Plate 68, figs. 407 and 408. Chart 272.) 



Histological Characteristics. In form the grains are simple and mostly isolated. They fre- 

 quently occur in aggregates of two or three or more grains of equal or unequal size, and such aggre- 

 gates may be spherical. Nearly all the isolated grains are 

 marked at the distal end or at other parts by one or more 

 well-defined pressure facets, usually three or four. The 

 surface of the grains is quite regular, but shapes vary, 

 owing to differences in the number, size, and arrangement 

 of the pressure facets. The conspicuous forms are hemi- 

 spherical with a 2-, 3-, or 4-faceted base, the rounded end 

 being the proximal ; also spherical aggregates consisting of 

 two or three grains, and forms which vary in accordance 

 with the peculiarities of the pressure facets. The grains 

 are not flattened, and on end they usually appear spherical. 



The hilum is usually not distinct, but when it can 

 be seen it appears as a comparativelj' large round spot, 

 centric or eccentric up to about two-fifths of the longi- 

 tudinal axis and in the median line. It is never fis- 

 sured, though two lines may sometimes appear to extend 

 from it to the corners of the facets, but this appearance 

 is probably due to a depression at the facet. There are 

 no multiple hila. 



The lamellce are indistinct, regular, coarse rings, 

 having the form of the outline of the margin; slightly more distinct in some grains than in others, 

 but do not vary much in distinctness in the same grain. There are about 6 on the larger grains. 



The grains vary in size from 3 to 26ai. The common size is 16/i. 



Polariscopic Properties. The figure is centric or somewhat eccentric. The two lines extending 

 to the corners of the facets are clear-cut, the other two are not. Often all the lines are broad and 

 not clean-cut and widen towards the margin. The lines are straight, but of varying lengths, and 

 are generally placed at varying distances from one another. 



The degree of polarization is fairly high. It varies much in different grains (being low in some 

 and high in others) and also in various parts of the same aspect of a grain, usually being low near 

 the facets, and it also varies in different aspects of a grain. 



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

 The colors are often pure. 



Iodine Reactions. ^Yith 0.25 per cent Lugol's solution the grains color a fairly deep violet 

 which deepens rapidly; with 0.125 per cent solution they color lightly, but the color deepens rapidly. 

 After heating in water until the grains are completely gelatinized, the solution is colored fairly and 

 the grains deeply on the addition of iodine. After boiling for 2 minutes the solution is colored 



Curve of Reaction-Intensities of Starch of 

 Gladiolus byzantinus. 



