228 BOTANICAL MICROTECHNIQUE. 



is also finally decomposed by chloral hydrate, and that very 

 small amounts of starch, which are naturally first attacked, 

 may be easily overlooked, if the sections are not examined 

 soon after the addition of chlorate hydrate. 



The action of chloral hydrate may be hastened by heating, 

 but the color of the starch, due to iodine, thereupon disap- 

 pears, to reappear on cooling again. 



Eau de Javelle ( 12,4), recommended by Heinricher (I) for 

 the recognition of starch, acts in the same way as chloral 

 hydrate. But, according to this author's statements, it 

 is better to treat the objects with it before the addition 

 of iodine, since otherwise the iodine hinders the destruction 

 of the protoplasm. 



Both media, chloral hydrate and eau de Javelle, may be 

 used with advantage when it is desired to demonstrate the 

 distribution of starch in large organs, like whole leaves. It 

 is best, in this case, to place the objects in a concentrated 

 solution of chloral hydrate containing iodine, and to heat 

 them to boiling in it. In this way leaves at all delicate may 

 be cleared and saturated with iodine in a few minutes. 



406. The recognition of starch may be accomplished with 

 greater certainty in microtome sections. For this purpose, 

 it is best to use a very concentrated solution of iodine and 

 iodide of potassium, which stains the smallest starch-grains 

 dark violet or quite black. These then stand out sharply, 

 even in cells rich in protoplasm, from the brown proteids. In 

 doubtful cases, a concentrated chloral hydrate solution may 

 be afterwards added, in which the starch-grains swell and 

 become of a beautiful blue color, while the rest of the cell- 

 contents suffer a wide-reaching destruction. 



407. I will remark here that not all starch-grains are 

 colored blue by iodine. But there are some which are 

 colored wholly or in part red by iodine, or which take 

 intermediate colors between red and blue. It is probable, 

 according to the researches of Shimoyama (I) and A. Meyer 

 (I), that the varying behavior of these starch-grains is due 

 to the fact that they contain greater or less quantities of 

 amylodextrine and dextrine besides true starch. 



