30 HERRE 



may never be found elsewhere. The climatic conditions which cause 

 this have already been discussed by the author elsewhere. Yet these 

 same climatic conditions also give us an exceedingly diversified lichen 

 flora, and it is believed that the present work can therefore be used 

 as a manual for the identification of lichens over a great part of the 

 western half of the United States. 



In taking up the study of lichens, while the habit and general 

 macroscopic structure is of importance and nothing can quite take 

 the place of careful field work, the student must also be careful and 

 accurate in the microscopic examination of all material. For this 

 examination careful sections should be made both of thallus and fruit. 

 A comparison of sections of the thallus of two plants may show con- 

 stant differences when the fruit is similar in structure. The algae, 

 too, need special attention, since some of the features relied upon by 

 algologists may be absent when living under the conditions found 

 within the lichen thallus. This is especially true of some of the fila- 

 mentous blue-green algae. 



As a corroborative test in the determination of species, one often 

 finds certain chemical tests of considerable value. For this purpose 

 a bit of the cortex, medulla, or apothecium is subjected to the action 

 of potassium hydrate, or KOH, using a 25 per cent or 50 per cent 

 solution. In the same way a saturated solution of calcium chloride, 

 CaCl 2 O 2 is used, either by itself or applied immediately after KOH. 

 The ordinary solution of iodine used in the botanical laboratory, 

 designated as I, is used frequently, most often in the examination 

 of sections of apothecia. 



Results of the above tests are not to be considered as sufficient to 

 separate species when there are no other differences, but are secondary 

 characters, to be considered with other characters based on structure 

 or primary differences. Personally, the author has found the tests 

 to be quite uniform and reliable, even when examining specimens 

 obtained from regions thousands of miles apart, or growing on dif- 

 ferent substrata. 



In examining the spores of lichens, the beginner or general student 

 must be cautious about observing and measuring any spores which 

 may happen to be within the field of the microscope. In addition to 

 the spores of various fungi which occur on the surfaces of all plants, 

 the thallus of some lichens is frequently infested with parasitic fungi, 



