GENERA HOMERIA AND TIGRIDIA. 711 



one-third are gelatinized in 4 hours, while others are unaltered. The hilum becomes distinct, and 

 the distal end and the most prominent parts of the margin become dark. This process extends over 

 the grain, with some swelling, usually very regular. There is a very sharp line of demarcation 

 between the gelatinized and ungelatinized portions of the grain. The whole grain is finally dark- 

 ened. The swollen grains formed are not very large and are generally smooth and somewhat irreg- 

 ular, but retain much of the original form of the grain and are of an even color throughout. 



With chromic acid there is a slight reaction in a few grains in 13^ minutes; it is in general in 2J^ 

 minutes, and over in 15 minutes. The hilum becomes very prominent and the grain is covered 

 with striae; its inner portion is altered into a gelatinous mass. The substance at the margin forms 

 a thin ring (very distinctly striated and ragged on the inner edge), which becomes thinner and more 

 transparent and is finally dissolved at one point, from which the inner gelatinized mass flows out 

 and is dissolved, followed by solution of the other parts. 



The reaction with pyrogalUc acid begins very slowly, and there is only a slight reaction in some 

 grains in 10 minutes. It is general in 15 minutes, and all are partially gelatinized in an hour. A 

 few are completely gelatinized in 85 minutes. The reaction consists, as with chromic acid, in the 

 appearance of fine striae throughout the grain, the dissolution of the inner part of the grains, and the 

 formation of a comparatively thin, distinctly striated, marginal ring that is very ragged on the inner 

 side. This ring becomes clearer and thinner as the grain swells until it forms merely a thin, trans- 

 parent film. The gelatinized grains are fairly large and somewhat wrinkled, but are generally 

 smooth and not greatly distorted and retain much of the original form of the grain. 



With ferric chloride a few grains react and some are fully gelatinized in 5 minutes. One-half 

 are affected, including all the smaller (most of which are fully gelatinized), in 25 minutes. About 

 five-sixths are fully gelatinized, but the others are affected, in an hour. The reaction consists in the 

 dissolution of the inner portion of the grain, preceded by the appearance of fine striae throughout, 

 the swelling of the grain, and the formation of a thin, ragged, striated marginal ring, which gradually 

 becomes very thin and transparent. The swollen grains are fairly large, somewhat wrinkled and 

 distorted, but usually retaining somewhat the original shape of the grain. 



With Purdy's solution one or two grains show some reaction in 45 minutes. There is no further 

 change. Similarities in the properties of the starches of Morcea and Homeria are very apparent. 



GENUS TIGRIDIA. 



This genus includes about 8 or 10 species of bulbous plants, natives of Mexico, Central America, 

 Peru, and Chili. It was for many years identified with Ferraria, a South African genus, and even at 

 present the typical species, T. pavonia, is referred to in Mexico as Ferraria tigridia. Tigridias are pop- 

 ularly known as the Mexican tiger-flower, or tiger-iris, or shell-flower. The starches of T. pavonia 

 var. grandiflora alba Hort. and T. pavonia var. conchiflora Hort. {T. conchiflora Sweet) were studied. 



STARCH OF TIGRIDIA PAVONIA VAR. GRANDIFLORA ALBA. (Plate 68, figs. 403 and 404. Chart 270.) 



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

 no pressure facets were observed. Irregularities are frequent, owing to the unequal development 

 of the surfaces and margins, chiefly in the form of nodular or nipple-like protrusions. Depressions 

 of the margin near the proximal end often give this part of the grain an appearance of protrusion. 

 The small grains are of variable shapes, chiefly rounded, ovoid, elliptical, triangular, and polygonal. 

 They are very numerous in comparison with the number found in most starches. The conspicuous 

 forms are the lima-bean-shaped, reniform, oval, and ovoid; also rounded and lenticular-shaped and 

 various modiflcations of the foregoing. The grains are somewhat flattened and about one-half to 

 two-thirds as thick as they are broad. 



In the larger grains the hilum is deeply and irregularly fissured, and in the grains of medium size 

 it appears as a distinct, comparatively large, round spot. It is eccentric from two-fifths to one- 

 fourth, usually about one-third, of the longitudinal axis. There are commonly many deep but 

 narrow and irregular fissures of varied arrangement. In many grains fissures radiate from two or 

 more centers, and in some the substance of the grain between the hilum and the distal end is fis- 

 sured irregularly, which may mean a number of hila, but it is impossible to definitely determine this. 



The lamellcB are not distinct circles, ellipses, or arcs of circles. When they can be distinctly 

 made out they appear rather coarse near the hilum, and fine as they are located nearer the margin 

 47 



