INTRODUCTION. ix 



in presenting, in succession, pairs of opposite characters^ 

 between which the student is to choose, by a comparison 

 with the plant, till the required genus or species be 

 found. Suppose, for example, that he takes Polytri~ 

 chum piliferwn as the object of his examination. On 

 having recourse to the TABULA GENERUM, he will see 

 by examining the mouth of the capsule that it will not 

 accord with the first, but with the second character there 

 given, " Peristoniio instructo" which carries him to 

 No. 7, where he will again compare his plant with the 

 other character, and will be referred to No. 8. Here 

 he will have no difficulty in discovering whether the 

 peristome be single or double, and will consequently 

 be carried on to No. 9, where he will with equal facility 

 decide upon that character which allows more than four 

 teeth to the peristome; and on being referred to No. 10, 

 the second line leads his eye to No. 1 1, where the words 

 " dentibus apicibus connexis" are applicable only to the 

 plant in question; and then going on to No. 12, the 

 character against POLYTRICHUM will be found to be the 

 only one which will suit his plant. On referring to 

 the species under the genus Polytrichum in the con- 

 tinuation of the Tabula, it will be seen that, having a 

 calyptra covered with hair-like processes, it will belong 

 to that character which refers to No. 3, when an exami- 

 nation of the leaves will be necessary to decide upon 

 what we are to choose. These leaves having their mar- 

 gins involute, we go to No. 4, where, finding our plant 

 to have diaphanous points to the leaves, we cannot he- 

 sitate in naming it P.piliferum. The same plan must 

 be adopted in the determination of any other species. 

 With regard to our Synonyms, we have endeavoured to 

 get them into as small a space as was possible, consist- 



