xxviii INTRODUCTION 



species is a morphological rather than a physiological unit, and it is not the 

 structures but the cell-products that are affected by reagents. Those most 

 commonly in use are saturated solutions of potash and of bleaching-powder 

 (calcium hypochlorite). The former is cited in text-books as KOH or simply 

 as K, the latter as CaCl or C. The C solution deteriorates quickly and 

 must, therefore, be frequently renewed to produce the required reaction, 

 i.e. some change of colour. These two reagents are used singly or, if con- 

 jointly, K followed by C. The significance of the colour changes has been 

 considered in the discussion on lichen-acids. 



Iodine is generally cited in connection with its staining effect on the 

 hymenium of the fruit; the blue colour produced is, however, more general 

 than was at one time supposed and is not peculiar to lichens ; the asci of 

 many fungi react similarly though to a less extent. The medullary hyphae 

 in certain species also stain blue with iodine. 



