COLLECTION, PRESERVATION, AND EXAMINATION. Ill 



mens which will exhibit the fertile and sterile conditions of 

 the plant, — both surfaces of the thallus, varieties depending 

 on differences of habitat, — and monstrosities, if any."* 



The use of various chemical reagents is a most important 

 auxiliary to the examination of the tissues of Lichens under 

 the microscope. One class of chemical substances is use- 

 ful on account of the colour which they strike with the cel- 

 lulose, amylaceous, and other matters of which the consti- 

 tuent cells of these tissues are composed, or which they 

 contain ; the other, from their power of dissociating certain 

 elements of these tissues which are intimately united — of 

 rendering distinct the outlines and structure of various 

 delicate and transparent cells, and of coagulating their con- 

 tents. Of the former class the most useful reagent is 

 Iodine, in the form of the ordinary tincture of the drug- 

 gist ; of the latter, Sulphuric and other mineral acids : with- 

 out their aid the student will frequently fail to discover 

 certain elements or tissues, which are either very delicate 

 and transparent or very minute and colourless. We should 



# The student cannot satisfactorily examine the external characters of the 

 thallus and its fructification without the aid of a simple pocket-lens, which 

 may be had at any optician's, for one or two shillings. — Eor directions as to 

 the application of the compound microscope, we must refer the uninitiated to 

 works treating of the construction and uses of that most valuable instrument. 



