1 66 BOTANICAL MICROTECHNIQUE. 



derivatives. When the tissue is transparent enough, the 

 ammonia may be neutralized with acetic acid, and the tissue 

 placed in the staining fluid.] 



291. The behavior of callose with iodine reagents, which 

 has been exactly determined only for the callose pa.ds of 

 sieve-tubes, is also characteristic, and, according to Lecomte 

 (I, 268), best brings out their intimate structure. Chloro- 

 iodide of zinc stains callose brick-red or red-brown according 

 to the proportion of iodine it contains, calcium chloride and 

 iodine solution (cf. 246, 5) stains it rose-red, or wine-red 

 after previous staining with aniline blue, while the sieve- 

 plates are colored violet. 



8. Pectic Substances. 



292. Mangin (IV-VI) has lately shown microchemically 

 that pectic substances (pectin, pectose, pectic acids) are very 

 widely distributed in the cell-walls of the most different 

 plants, and that they form especially the so-called intercel- 

 lular substance of unlignified and unsuberized membranes. 



293. For the microchemical recognition of pectic sub- 

 stances Mangin uses (IV and VI) chiefly various coloring 

 matters, phenosafranin, methylene blue, Bismarck brown, 

 fudisin, Victoria blue, violet de Paris (= methyl violet B), 



and rosolan (= mauvein), and others. These do not color 

 pure cellulose, but do stain pectic substances, as well in 

 neutral solution as after slight acidification with acetic acid. 

 But lignified and suberized membranes are also stained by 

 these dyes. However, there remains a distinction between 

 them and pectic substances in that the latter are quickly 

 decolorized by alcohol, glycerine, and acids, while the for- 

 mer retain their color in these fluids. Mangin also gives a 

 number of dyes which leave pectic substances uncolored in 

 a neutral solution, while they deeply color lignified and 

 suberized walls. Such colors are : acid green, acid brown, 

 nigrosin, indulin, the croceins, and the ponceaux. Mangin 

 obtained instructive double stainings by mixing one of these 

 dyes with one of the previous group. 



On the other hand, Mangin (V) has lately named a num- 



