272 TRANSACTIONS AND PROCEEDINGS OF THE [Sess. lxvii. 



The past and present distribution of each species should 

 be ascertained in a very much more systematic way than 

 has yet been done, or, except in a few cases, even 

 attempted, the habitats should be indicated, and the 

 frequency should be recorded on some definite scale. 

 Absolute accuracy cannot be expected ; but it should 

 be possible to reach a degree such as to permit of the 

 records being used by later workers as a scale by which 

 to determine the changes that show themselves as the 

 years go by, and perhaps to afford evidence of the causes 

 that bring about these changes, both of increase and of 

 decrease or extinction, of gain and of loss. A method 

 that I have made use of to record the changed condition 

 of the vegetation from year to year on made-up ground, 

 and other places near Aberdeen, I have found very useful 

 on limited areas, where a complete record of the species 

 observed was kept, and the rarity or abundance of each 

 was marked by a scale from 1 to 4, denoting rare, common, 

 frequent, abundant, each also modified by the signs 

 — and +. Thus I used twelve grades, from 1 — , 

 denoting extremely rare, to 4 + , denoting abundance to 

 the exclusion of other species. I found it possible in this 

 way to follow with confidence rapid changes in the relative 

 proportions of the species, and also to record the incoming 

 of species new to a locality, and could follow the struggle 

 among the various forms until a relative equilibrium was 

 reached. 



For larger areas other methods have been employed. 

 Buchenau, for example, in his "Flora der nordwestdeutschen 

 Tiefebene" (1894), employs signs to distinguish four grades 

 in the relation of plants to the district, viz. ^ characteristic 

 species ; * confined to certain limited habitats, e.g. sea- 

 coast, etc.; '[ species of middle or east Germany that have 

 overpassed the south or east boundary of the north- 

 west German plains ; -|- adventitious plants, relatively 

 late introductions, or immigrants. 



It is evident that the usual indications of frequency 

 (frequent, common, rather local, etc.) are defective, as 

 they do not indicate clearly the relative frequency of 

 localities and of individual plants within these localities. 



W. Schemmann, in " Beitriige zur Flora der Kreise 



