750 



STARCHES OF IRIDACB^, 



NOTES ON THE STARCHES OF CROCUS. 



There are some minor differences in these starches in regard especially to the relative number of 

 different forms of grains, the hilum, and the lamella, which are useful in distinguishing one from the 

 other. In general, C. srisianus and C. var. (Baron von Brunow) have the closest Ukeness of any two. 

 In the reactions, the starches are very much alike, the main differences being noted in the tempera- 

 tures of gelatinization (5°), and in the reactions with chloral hydrate-iodine and ferric chloride. 



GENUS ROMULEA. 



The genus Romvlea includes about 33 species of cormous plants that are closely allied to Crocus, 

 and which are natives of the Mediterranean region and of Western and Southern Africa. Romulea 

 rosea var. spedosa Baker {Tricnonema spedosum Ker.) was the only specimen available to us as a 

 source of starch. 



STARCH OF ROMULEA ROSEA VAR. SPECIOSA. (Plate 75, figs. 447 and 448. Chart 292.) 



Histological Characteristics. — In form the grains are simple, and are isolated except a few aggre- 

 gates which are usually in the form of doublets or triplets. Nearly all the isolated grains are marked 

 by one to three pressure facets. There are a few clumps. The surface is usually smooth and regular. 

 The conspicuous forms are the hemispherical to dome-shaped with one to three facets at the base, 

 the spherical, and the ovoid; also some polygonal forms that owe their shape to multiple pressure 

 facets. The grains are not flattened and on end they appear spherical. 



The hilum is a distinct, comparatively large spot, usually slightly eccentric and in the median 

 line. In some grains there appears to be a cavity at the hilum. The hilum is rarely fissured. Double 

 and triple hila may occur. 



The lamellm are rather coarse, usually indistinct, regular, and continuous, and follow the marginal 

 outline closely. There is one lamella which is near the hilum and one or two near the margin, which 

 are coarser than the rest and very distinct. Seldom more 

 than 6 can be counted on a single grain. 



The grains vary in size from 3 to 25/t. The com- 

 mon size is about 15/x. 



Polariscopic Properties. — The figure is usually eccen- 

 tric, distinct, and fairly clear-cut It is modified by the 

 surfaces of the facets. Its lines are rather broad, tending 

 to become broader marginally, and are sometimes bent. 



The degree of polarization is fairly high. It varies 

 somewhat in different grains and in different aspects of 

 a ^ven grain. 



With selenite the quadrants are well defined, usually 

 clear-cut, and unequal in size. The colors are fairly pure. 



Iodine Reactions. — With 0.25 per cent Lugol's solu- 

 tion the grains color a very light violet-blue and the tint 

 deepens slowly, becoming fairly deep after some time; 

 with 0.125 per cent solution the grains color very faintly 

 and the tint deepens slowly. After heating in water until 

 all the grains are gelatinized the solution colors fairly and 

 most of the gelatinized grains deeply. After boiling for 

 2 minutes the solution is colored very deeply and the grain-residues lightly. The capsule is colored 

 violet with an excess of iodine and most of them contain some blue-reacting substance. 



Staining Reactions. — ^With gentian violet and with safranin the grains begin to color slightly 

 at once and at the end of 30 minutes they are very lightly stained. 



Temperature Reaction. — The temperatiu'e of gelatinization is 73° to 74° C, mean 73.5°. 



Effects of Various Reagents. — ^With chloral hydrate4odine reaction begins in a very few grains in 

 1}^ minutes and is general in 4 minutes; about one-fourth, including all the small grains and a very 

 few of the large grains, are gelatinized in 25 minutes, and about half of the larger grains are gelatin- 

 ized in 1 hour 35 minutes. The reaction begins at the corners and edges of the facets, and the starch 



Curve of Reaction-Xntensities o£ Starch of Romulea rosea 

 var. speciosa. 



