HO BO TA NIC A L MICRO TE CHNIQ UE. 



cell-wall, and never occur in the cell-contents ; so that it 

 must be supposed that they are formed directly in the wall. 



Gloeocapsin is red or blue, and becomes red with hydro- 

 chloric acid (rose-red, reddish orange, or bluish red), and blue 

 or blue-violet with caustic potash. It occurs chiefly in Glcco- 

 capsa. 



Scytonemin gives a yellow to dark-brown color to the 

 membranes of Scytonema and various other algae. We have 

 recent studies of its characteristics by Correns (I, 30). 

 According to these, it is especially distinguished by taking" 

 a blue-violet color, greatly resembling that which appears in 

 the cellulose reaction, with chloroiodide of zinc, or with iodine 

 and sulphuric acid. Scytonemin is destroyed by eau de 

 Javelle (cf. 12, 4), and threads so treated no longer give 

 the above-mentioned reactions with iodine. 



With acids scytonemin takes a green color which is 

 restored to the original color on the neutralization of the 

 acid. Even sulphurous acid acts in this way and does not 

 destroy the pigment. 



Alkalies color it more red-brown. Sheaths which had 

 been treated with caustic - potash, although the pigment 

 appeared unchanged after the potash was washed out, no 

 longer took the violet color with chloroiodide of zinc, accord- 

 ing to Correns. No macrochemical studies of the compo- 

 sition of these substances have been made. 



IpO. Very numerous and various pigments occur in the 

 membranes of the fungi, according to the investigations of 

 Bachmann (II) and Zopf (V). But, since these have hitherto 

 been studied almost exclusively in their macroscopic rela- 

 tions, and very little has been established as to their chemi- 

 cal composition, the student may be referred to Zopf's 

 account of them (II, 418). 



191. The pigments deposited in the membranes of the 

 lichens have lately been studied by Bachmann (IV). He 

 distinguishes by their microchemical behavior sixteen differ- 

 ent pigments, whose chief reactions are shown upon the 

 table on the next page. 



