18 TRANSACTIONS AND PROCEEDINGS OF THE [Sess.lxv. 



cases being simply a continuation of former processes, in 

 some others a reversion in the direction towards the previous 

 conditions. The change in the flora during the short time 

 of a century must rarely be capable of proof, except with 

 those brought about through the influence of man, but this 

 change has probably been greater in the Highlands during 

 the last hundred years than in any other part of Britain. 



In every country it is probaV)le that the relative frequency 

 of every species of plant is always altering, but this change 

 is, in normal conditions, usually of too slow a nature to be 

 noted except in a very limited locality. It requires accurate 

 observations to be made, in order that succeeding botanists 

 may profit by the work of those of an earlier time, and 

 even at the present time one cannot help observing the 

 usually vague manner in which the quantity in which 

 species occur is stated. As there is so much difference 

 in the degree of frequency at which plants occur, it is of 

 course difiicult to define this degree with what must 

 necessarily be only a few terms ; but I think that definite 

 terms might always be used, so that there would be no 

 mistake as to what an author intended by the use of the 

 term he applied. A few progressive numerals, with a 

 distinct meaning, might be attached to such words as 

 " common " and " rare," which would enlarge their signi- 

 fication and yet remain definite. 



There is evidence, I think, that some species are 

 decreasing naturally in a more rapid manner than would 

 be expected without being exposed to evident competition 

 with other plants, but it is difficult to understand if this be 

 the case why the plant is not already extinct. A case in 

 point is Cephalcuithera ensifolia. In Scotland it is rare and 

 local, occurring in widely separated districts, with only a 

 few plants in each locality. 



This may be taken as the sign of a species when native 

 once more widely spread, in this case probably when the 

 clmiate was warmer, but which is now decreasing. In 

 a-idition to this, in the district in which it occurs, where I 

 know it, it does not appear to form seed in its native site, 

 or when transplanted into the garden ; and although it 

 glows on good soil and is sheltered, it is a much smaller 

 plant than south of England specimens which I have seen. 



