376 



STARCHES OF GRAMINACE^. 



Iodine Reactions. — With a 0.25 per cent Lugol's solution the most of the grains color a very 

 light old-rose, a very few take on a deep reddish-purple, while some do not color at all; with a 

 0.125 per cent solution the grains color a light old-rose, which in 5 minutes has become fairly deep. 

 It is lighter and much redder than in grains of Avena. After heating in water until all are gelatin- 

 ized, the solution does not color at all, but the gelatinized grains color a very deep purple, rather 

 darker than in Avena. After boiling for 2 minutes, the 

 solution colors a very dark bluish-purple and the grain- 

 residues a very light old-rose tint. When an excess of 

 iodine is added the capsules assume a deep wine-red color. 



Staining Reactions. — With gentian violet the grains 

 begin to stain very lightly at once and in 30 minutes 

 they are lightly stained, the color being the same as 

 that of Avena. 



With safranin the grains begin to stain very lightly 

 at once and in 30 minutes they are lightly stained, the 

 color being the same as that of Avena. 



Temperature Reaction. — The temperature of gelatin- 

 ization is 59.5° to 61° C, mean 60.25°, 



Effects of Varioiis Reagents. — ^With chloral hydrate- 

 iodine most of the grains begin to react in 45 seconds ajid 

 the reaction is over in 10 minutes. It is the same quali- 

 tatively as that of Avena. 



The reaction begins at once with chromic acid and 

 is over in dO seconds. It is so rapid that it is not pos- 

 sible to distinguish the separate steps. 



The reaction with pyrogallic acid begins in 30 to 45 seconds, and is over in 5 minutes 

 the same qualitatively as that of Avena. 



With ferric chloride the reaction begins in a few grains in 13^ minutes and is over in 10 minutes. 

 It is the same qualitatively as that of Avena. 



With Purdy's solution there is a slight reaction in a few grains in 2 minutes. About one-fifth 

 are completely gelatinized in 15 minutes and about two-fifths in 40 minutes. There is little further 

 change in an hour. It is the same qualitatively as that of Avena. 



Curve of Reaction-Intensitiea oi Starch of Arrhenathenim 

 elatiua var. 



It is 



NOTES ON THE STARCHES OF GRAMINACEvE. (Charts 22 to 30.) 



Comparing the gross histological peculiarities of the starches of the different genera, it will be 

 seen that there is a distinct grouping, as instanced in Zea and Andropogon, Triticum and Secale and 

 Hordeum, and Avena and Arrhenatherum, respectively. The types of the starch-grains are distinctly 

 different in all three groups: In Zea and Andropogon the grains are essentially polygonal; in the 

 Triticum group they are essentially in the form of large, round, ovoid, and oval disks; and in the 

 Avena group the type is polygonal with few large round, ovoid, and ov.il disks. Comparing the 

 reaction curves it will be noticed that the same marked group relationships are strikingly exhibited, 

 except of a single reaction in each in the case of Secale and Triticum of the Triticum group. The 

 curves of Zea and Andropogon closely correspond; those of Panicum and Oryza, respectively, which 

 represent different genera, are modifications of the preceding; those of the Triticum group are in 

 accord with the exception of Secale, in which there is shown a distinctly higher reactivity with 

 chloral hydrate-iodine, and of Triticum, in which there is a distinctly higher responsivity with 

 Purdy's solution than is observed with the other members; while those of the Avena group are 

 nearly alike, Botanically, the relationships of Zea and Andropogon are recognized especially in 

 the fact that they are among the few grasses that have a solid stem; and the relationships of the 

 Triticum and Avena groups, respectively, are well marked. The Graminaceas starches do not 

 exhibit in their reactions the generic diversities which commonly are conspicuous in the starches 

 of the seeds of Leguminosoe and in those from genera that have been obtained from parts other 

 than seeds, such as bulbs, tubers, rhizomes, root-stocks, etc. 



