XV 



gr. j. ; Iodide of Potash, gr. iij ; Distilled water, £ oz., which must 

 be kept in a glass-stoppered bottle of dark -coloured glass, or covered 

 with tinfoil to exclude light. In using this test, the section of 

 the apothecium must be placed in the iodine solution at once, and 

 not previously in the hydrate of potash, which would nullify the 

 re-action. To test the thallus either on its cortical layer, or in 

 the medulla, hydrate of potash is used, compounded of equal 

 weights of caustic potash and water. Hypochlorite of lime 

 (chloride of lime and water) is another reagent, which may be made 

 of any strength. These are applied by small brushes made of spun 

 glass, one brush being kept exclusively for each reagent, and also 

 a separate vessel used for each. The modus operandi is this : touch 

 the cortical layer or the medulla (exposed by scraping off a morsel 

 of the cortical layer) with the hydrate of potash, and while 

 still moist apply the hypochlorite of lime, and note whether any 

 re-action, and of what kind, results. Sometimes the hydrate of 

 potash produces a distinct yellow tinge, which may be symbolised 

 as (K+) or if only faint as (E f-f) This yellow re-action is 

 sometimes persistent (K+), but in other lichens immediately 

 changes to a red colour (K yellow then red). In others the yellow 

 produced by the hydrate of potash is changed into red, or the 

 yellow is deepened, by the immediate application of hypochlorite 

 of lime, symbolised (K yellow C red) or (K yellow, C deep-yellow). 

 Again the hydrate of potash may produce no re-action, but the 

 immediate subsequent application of hypochlorite of lime elicits 

 red or yellow as the case may be, symbolised thus (K - C + red) or 

 K — C + yellow). Sometimes neither reagent produces any re-action 

 and is thus noted (K - C - ). A very convenient mode of symbol- 

 ising the re-action of the cortical layer and medulla of the same 

 lichen is to place the re-action of the former above that of the 

 latter thus (K+=C). These re-actions, which may be generally 

 obtained on any portion of the thallus, are frequently more vivid 

 on the younger or circumferential portions. Success depends on 

 the reagents being freshly compounded and of the proper strength, 

 and temperature has also something to do with it, as in very 

 severe cold weather the re-action takes place very slowly and im- 

 perfectly, and perhaps at all times it would be advisable to warm 

 the reagent. Great cleanliness must be observed with the brushes 

 and vessels, which should be thoroughly wiped dry after using. 

 None of the liquid reagent should be left exposed to the air from 

 one day to another, nor a fresh supply added to any which has 

 been so exposed, nor must any which has been once used be 

 returned to the stock bottles, which should always have close fit- 

 ting glass-stoppers. Neglect of these precautions results in failure 

 and uncertainty. The aqueous solution of iodine is also useful as 

 a test on the exposed medulla in certain cases. 



The following work is arranged as to Families, Tribes, and 

 Genera, with some slight modifications, on the system of Dr. W. 

 Nylander, of Paris, as being simple and philosophical, founded on 



