890 



STARCHES OF GESNERACE^ AND CUCURBITACEiE. 



few refractive granules at the distal end. The gelatinized grain is much swollen and is slightly- 

 distorted at the distal end, but the outline has a general resemblance to imtreated grains. 



NOTES ON THE STARCHES OF GESNERACE^. 



The starches of Gesneria and Gloxinia exhibit histological peculiarities as regards form, hilum, 

 lamellae, and size that render them easily distinguishable. In their reactions they differ definitely 

 in every one, excepting with ferric chloride. Gesneria is recorded as having a lower degree of polari- 

 zation, a higher reactivity with the anilmes, a lower temperature of gelatinization (4.75), and less 

 sensitivity to all of the chemical reagents except ferric chloride. 



STARCHES OF CUCURBIT ACE/E. 



Class, Monocotyledones . Order, Campanulales . Family, Cucurbitacefe . 



represented, Trianosperma. 



Genus 



The Cucurbitacem include about 80 genera and 600 species. Most of them contain an acrid 

 principle and in some this is present in sufficient quantity to render them acrid poisons. Some are 

 used medicinally; others jaeld fruits, such as the cucumber, water-melon, pumpkin, etc., which are 

 used as foods; and some are cultivated as garden plants. 



GENUS TRIANOSPERMA. 



This small genus is native chiefly of Brazil and the West Indies; one is from the Old World, 

 from tropical Africa. The plants have thick, fleshy roots, which contain much starch. A prepara- 

 tion was obtained from T. ficifolia and studied as a type of the genus. 



STARCH OF TRIANOSPERMA FICIFOLIA. (Plate 98, figs. 587 and 588. Chart 393.) 



Histological Characteristics. In form the grains are usually simple, with occasional compound 

 grains and some small aggregates ; nearly all have one or more large, clear-cut pressure facets. The 

 surface is rounded and regular in outline, except when 

 altered into irregular forms by pressure facets. The con- 

 spicuous forms are the dome-shaped to hemispherical, 

 ovoid, round, pyriform, lenticular, quadrangular and 

 polygonal, and indefinite forms. 



The hihwi is a very distinct, comparatively large, 

 round spot, centrally or somewhat eccentrically placed 

 and usually in the median line. At times it appears as a 

 round cavity. It is sometimes fissured deeply, radially 

 or irregularly. Rarely it is marked by a clear-cut cross 

 or by a small transverse or diagonal fissure. 



The lamelke are very distinct, coarse, circular, and 

 regular, and do not generally follow the outline of the 

 margin, except when very near it. There is usually one 

 very prominent lamella about halfway between the hilum 

 and the margin. There are about 5 to 8 lamellae on the 

 larger grains. 



The grains vary in size from 3.5 to 26/^; the com- 



1 A ,. Curve of Reaction-Intensities of Starch of Trianosperma 



mon Size is 14,. (icifoUa. 



Polariscopic Properties. The figure is centric or 

 slightly eccentric, distinct, and usually clear-cut. One or two of the lines are usually broader and 

 less clear-cut than the others and usually straight, but tend to vary in thickness along their course. 

 The figure varies in distinctness in different grains. 



The degree of polarization is high. It is highest in the ovoid and round grains, varying some- 

 what in different aspects of a grain and also in parts of the same aspect of some grains. At the facets 

 it is low. 



