146 BOTANICAL MICROTECHNIQUE. 



255. According to Hegler (I, 40), all of these compounds 

 that have been tested give the same color-reactions with co- 

 niferin or vanillin or with a mixture of both substances ; and 

 this author therefore considers it demonstrated that both 

 compounds occur constantly in lignified membranes, and that 

 they are the cause of the above described color-reactions. 



Of the above enumerated reagents thallin and phenol de- 

 serve especial attention, since, according to Hegler (I), the 

 former gives the described color-reaction only with vanillin, 

 the latter only with coniferin.* Since thallin colors vanillin 

 yellow, but phenol colors coniferin blue, by the use of a mix- 

 ture of the two reagents one may draw certain conclusions 

 as to the relative abundance of the two substances, accord- 

 ing as the color produced is yellower or bluer. Hegler (I, 58) 

 has used for the same purpose a solution prepared by mixing 

 .5 gram of thallin sulphate, 1.3 grams of thymol, 2 ccm. of 

 water, 26.5 ccm. of alcohol, and .5 gram of potassium chlorate, 

 and diluted for use with its own volume of hydrochloric acid 

 of specific gravity 1.124. This author draws from his studies 

 carried on with this reagent, the conclusion that the younger 

 xylem-cells contain more coniferin than vanillin, but that 

 the older ones are rich in vanillin and less so in coniferin. 



256. On the other hand, it is to be noticed that, besides 

 vanillin and coniferin, other substances containing the alde- 

 hyde group give with the compounds mentioned identical or 

 similar color-reactions to those of lignified cell-walls ; accord- 

 ing to Ihl (I), cinnamic aldehyde, and, according to Nickel, 

 salicylic aldehyde. It may therefore be considered as good 

 as proven that the color-reactions of lignified membranes 

 depend upon the presence of one or of various compounds 

 belonging to the aldehyde group. SeliwanofFs observations 

 also support this view. According to these, lignified walls 

 are, on one hand, colored red by a solution of fuchsin decol- 

 orized with sulphurous acid, and, on the other hand, no 

 longer give the reactions of lignified membranes with phloro- 



* The correctness of Hegler's statement that thymol also gives no color 

 with vanillin has lately been disputed by Molisch (I, 48, Note 3). 



