COLLECTION, PRESERVATION, AND EXAMINATION. 113 



or destroyed thereby, that the latter may also appear blue ; 

 or the yellow colour of the contents, shining through the 

 transparent blue thecal membrane, may sometimes cause 

 these to assume a green tint. If iodine be applied to an 

 apothecium entire or sectioned, in consequence of this pe- 

 culiar reaction it is frequently possible to distinguish the 

 thecse by the naked eye in the form of a congeries of deep 

 blue lines or points; in some cases so abundant are the 

 thecse that the whole apothecium at once becomes blue. 

 By this means also the spore-sac is sometimes rendered 

 visible as a yellowish delicate membrane lining the theca. 

 The spores are generally coloured yellow, their outline and 

 contents rendered more distinct, and the latter, especially in 

 the old state, frequently coagulated and broken up. The 

 hypothecial tissue in most Lichens is also tinged blue. The 

 walls of the paraphyses, with the exception of the terminal 

 cell, which remains unaltered, appear of a very pale blue, if 

 the iodine is sufficiently dilute ; more usually this colour is 

 destroyed by that of the iodine, and they appear yellow; 

 their walls are more distinct, their septa become evident, 

 and their contents are coagulated and form an irregular core 

 or centre in the long axis of each constituent cell. The 

 spermatia are rendered more distinct by being coloured 



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