[2] 
The Sudden Appearance and Gradual 
Extinction of Certain Species of Plants in 
Linuted Areas. 
By G. A. GRIERSON.* 
N Wallace’s ‘‘Island Life” (p. 481) the following sentence 
occurs :—“‘ It is a well-known fact that fresh surfaces of soil 
or rock, such as are presented by railway cuttings and em- 
bankments, often produce plants strange to the locality, which 
survive for a few years, and then disappear as the normal 
vegetation gains strength and permanence.” Mr. Wallace makes 
use of the fact to show how the flora of one district may spread 
into another at a very great distance, and yet leave no trace of its 
progress. He mentions it as probable that it is in this way the 
Scandinavian flora has reached the southern hemisphere. Mr. 
Wallace attempts no explanation of the fact, but contents himself 
with citing numerous instances proving conclusively that it is so. 
We may, therefore, take it as an indisputable fact that plants 
do spring up in this way. In order to account for this apparently 
erratic distribution, it will be necessary to give correct answers to 
two questions: (1) Whence come the seeds which give rise to 
these plants? (2) Why do the plants so originated gradually die 
out in the majority of cases? In answer to the first question, 
there are two possibilities. Either the seeds pre-exist in the soil, 
but at too great a depth to germinate, and on the soil being turned 
over, as in the making of a ditch or railway-cutting, this obstacle 
is removed, and we have a repetition of the flora of an earlier 
period ; or the seeds are carried by the wind and germinate freely 
in the freshly-exposed earth, while those which fall on the sur- 
rounding over-crowded and comparatively exhausted soil, meet 
with an early death. The second question has, I think, only one 
possible answer : the soil becomes exhausted of the constituents 
most suitable for the growth of that particular species ; the species 
therefore becomes unfit to contend successfully with its better 
adapted neighbours, and, consequently, goes to the wall. 
In the absence of conclusive experiments, it is impossible to 
answer the first question with absolute certainty, and I would take 
the liberty of suggesting that some of our country pharmacists, 
* From Zhe Pharmaceutical Journal, 
