GENUS PISTJM. 



405 



Chart No. 46. 



I GV 

 S 



CI PA ( 

 POPS 



The grains var.v in size from the small, which arc 8 by Sn, to the larger round and ovoid forms, 

 whieh are 38 by 38^. The common size is 26 by 26//. 



Polnriscopic Properties. There is no true figure in the rosette grains, but there are portions 

 of figures confused with the lines of the fissures. In the grains of the bean type it corresponds with 

 the peculiarities described under Vicia and Phaseolus. 



The degree of polarization is low. It does not vary much in different grains. In the few grains 

 of the bean type it is fairly high. It does not vary much in different aspects of the same grain, 

 except when it is obscured by the fissures. It is slightly higher than in the green seeds. 



With selenite there are no quadrants, but poorly defined areas of blue and of yellow are grouped 

 together. In some grains the yellow and in some the blue predominates, according to their position 

 in the field. The colors are not pure. 



Iodine Reactions. With 0.25 per cent Lugol's solution the grains all color a fairly light violet; 

 with 0.12.5 per cent solution they color a light violet which deepens rather rapidly. The color is 

 the same as that of the green seeds. After heating in 

 water until all the grains are completely gelatinized, the 

 solution and the gelatinized grains color deeply on the 

 addition of iodine. After boiling for 2 minutes, the solu- 

 tion colors very deeply and the grain-residues a bright 

 blue. If an excess of iodine is added the solution becomes 

 a deep blue-green, and the grain-residues a rich reddish- 

 purple. After boiling for 5 minutes the shape of the 

 grains is still retained. The solution colors very deeply, 

 and some of the grain-residues color a bright blue and 

 others not at all when iodine is added. With an excess 

 of iodine the same results were obtained as noted for the 

 green seeds. 



Staining Reactions. With gentian violet the grains 

 when examined in masses show a very slight tint at once. 

 After remaining in the solution for 30 minutes they are 

 still very lightly stained. The coloration of the grain is 

 uneven, usually deeper along the course of the fissures. 

 Occasionally a verj' deeply stained grain is found. The 

 depth of staining is the same as of the green seeds. 



With safranin the grains when examined in masses show a slight tint at once. After remaining 

 in the solution for 30 minutes they are still very lightly stained. The coloration is uneven, usually 

 being deeper along the course of the fissures. The depth of staining is the same as that of the green 

 seeds. 



Temperature Reaction. The temperature of gelatinization is 74 to 75 C, mean 74.5. 



Effects of Various Reagents. With chloral hydrate-iodine the reaction begins at once. A few 

 grains are deeply colored in 30 seconds. The majority are gelatinized in 2 minutes, and practically 

 all in 5 minutes. After an hour those of the bean type remain ungelatinized. They are colored 

 a golden-brown by the reagent. The reaction is qualitativelj^ the same as in the green seeds. 



The grains begin to react at once with chromic acid. A few with stellate fissures are dissolved 

 in 20 seconds and all in a minute. All those of the bean type pass into solution in 5J2 minutes. The 

 reaction is qualitatively the same as in green seeds, but the grains with stellate fissures pass more 

 completely into solution, onlj' very little of the least refractive starch remaining. 



Reaction with pyroyallic acid begins at once. A few grains are gelatinized in 2Vi minutes, but 

 there is little if any further change after an hour. The reaction is qualitatively the same as that 

 noted for the green peas. 



Reaction with ferric chloride begins in 30 seconds. An occasional part of a broken-down grain 

 is gelatinized in 5 minutes, and a whole grain in 10 minutes. All are in process of reaction in 15 

 minutes, and the reaction is complete in nearly all in 30 minutes. After remaining in the reagent 

 for an hour there is little if any further change. The reaction is qualitatively the same as in the 

 green seeds. 



With Purdy's solution the grains begin to react in 30 seconds. .\11 are in process of reaction 

 in 15 minutes, and the reaction is complete in 30 minutes. After remaining in the solution for an 



Curve of Reaction-Intensities of Starch of Pisum 

 sativum var. (Eugenie, yellow). 



