886 



STARCHES OF CYCADACEiB. 



Differentiation of Certain Starches of the Genus Cycas. — Continued. 



Iodine Reactions. 

 Intensity and Color. 



C. revolula: Deep; blue-violet. 



C. drcinalis: Deep, the same as in C. revolula; blue-violet. 



Staining Reactions. 



WiUi Gentian Violet. 

 C. revoliUa: Deep. 

 C. curdnalis: Deep, the same as in C. revoltUa. 



With Safranin. 

 C. reoolxda: Very light. 

 C. drcinalis: Very light, the same as in C reodijia. 



Tehpebatubb of Gelatinization. 



C. revduta: 73 to 74° C, mean 73.5°. 

 C. circinalis: 71 to 73° C, mean 72°. 



Effects of Various Rbagentb. 



Reaction with Chloral Hydrate-Iodine. 



C. revolula: Begins in 1 to 3 or 4 minutes; complete in 



three-fourths in 45 minutes. 

 C. circinalis: Begins in from 1 to 3 or 4 minutes; com- 

 plete in almost all in 40 minutes. 



Effects of Various Reagents. — Continued. 



Reaction with Chromic Acid. 



C. revolula: Begins in 30 seconds; complete in 5 minutes. 

 C. circinalis: Begins in 45 seconds; complete in 3J^ 

 minutes. 



Reaction with PyrogaUic Acid. 



C. revolula: Slight reaction in IJ^ minutes; complete in 



nearly all in 30 minutes. 

 C. circinalis: Slight reaction in 1}^ minutes; complete 



in all in 25 minutes. 



Reaction with Ferric Chloride. 



C. revolula: Begins in 3 minutes; complete in 25 min- 

 utes. 



C. circinalis: Begins in 1 minute; complete in 25 min- 

 utes. 



Reaction with Purdy's Solution. 



C. revolula: Begins in a few in 7 minutes; only a very 

 few are completely gelatinized after 3 hours. 



C. circinalis: Begins in a few in 3 to 4 minutes; only a 

 very few are completely gelatinized in 134 hours. 



NOTES ON THE STARCHES OF CYCAS. 



Histologically the two starches are practically identical and in the reactions they so closely 

 correspond that such differences as have been recorded may fall within the limits of error of experi- 

 ment. 



GENUS DIOON. 



The genus Dioon of Cycads includes two species, both natives of tropical Mexico. The best- 

 known is D. edule Lindl.; D. tomenosum is a variable species. Dioon is stated to be the nearest of 

 the Cycadacece to the fossil plants belonging to this family. A starch is prepared from the seeds and 

 sold as a form of arrowroot. The starch used in this investigation was obtained from a specimen of 

 D. edule obtained from the Botanical Garden of the University of Pennsylvania. 



STARCH OF DIOON EDULE. (Plate 102, figs. 607 and 608. Chart 396.) 



Histological Characteristics. — Inform the grains are simple, with the exception of rare compound 

 grains of few components. There are a few aggregates and small clumps. The majority have well- 

 marked pressure facets. The grains are generally regular, but slight depressions and elevations of 

 the surface are not infrequent, and occasionally a nipple-shaped process near the hilum or a pointed 

 excrescence at either end of an ellipsoidal grain may be found. The most conspicuous forms are 

 round, nearly round, dome-shaped, elongated ovoid, ovoid, pyriform, and ellipsoidal. There are 

 also hemispherical, oyster-shell-shaped, polygonal and various irregular forms. 



The hilum is observed as either a clear, round, or elliptical spot usually eccentric about one- 

 third to one-sixth of the longitudinal axis, but centric in some of the round grains of fair size. The 

 hilum is generally not fissured, but a delicate transverse or diagonal cleft may intersect it; or a small 

 roimded cavity may be located at the hilum. 



The lameUce are often not demonstrable, but on some of the dome-shaped and ovoid grains it is 

 possible to count 10 which are rather coarse, complete rings. The shell-shaped forms, which are 

 few, have from 14 to 20 lamellae appearing as indistinct, complete circles near the hilum, and which 

 are probably incomplete and have the shape of the grain near the distal end. 



The grains vary in size; the smaller are 3 by 2ii; the larger dome-shaped ones are 18 by 16^; 

 the large ovoid are usually 20 by 14;u, rarely 32 by 18//, in length and breadth. The common size 

 of the dome-shaped is 12 by 10^ and of the ovoid 12 by 8/t in length and breadth. 



Polariscopic Properties. — The figure is usually eccentric. Its lines are rather broad, increasing 

 in width as they near the margin of the grain, and they generally intersect obliquely. They may be 

 straight, but often are bent and sometimes bisected. 



