54 BIO-GEOLOGY. 
such a barrier between species. Moritz Wagner has shown that, 
case of insects, a moderately broad river may divide two species of b 
or a very narrow snow-range two species of moths. | 
Again, another cause, and a most common one, is that the plan 
not spread because they find the ground beyond them already oc 
by other plants, who will not tolerate a fresh mouth, having onl 
enough to feed themselves. Take the case of Saxifraga hypnoides and 8. d 
umbrosa (London-pride). They are two especially strong species. 
show that, Mp especially, by their power of sporting, of div 
into Keine ; they show it equally by their power of thriving any 
if they ca only get there. They will both grow in any sandy g 
¿under a. ‘nal of only 23 inches, more luxuriantly than in their 
mountains under a rainfall of 50 or 60 inches. ‘Then how is itt 
ides ibm get down off the mountains, and that 
in Kerry it has got off the mountains and down to the sea-level, € 
m are too strong for them, and massacre their infants as soon 
And this brings us to another curious question,—the sudden and ab al 
dant appearance of plants, like the Foxglove and the Epilobium ang 
lium, in scm where they have never been seen before. Are their se 
as some think, dormant in the ground, or are the seeds which have g 
nated fresh ones wafted thither by wind or othe rwise, and a ible 
rminate in that one spot because there the soil is clear? 
pas mak; being scattered, could travel with the wind; that the plan 
appearance first on the new banks, landslips, clearing 
ber: it had nothing to compete against ; ; and that the Fostion did 
sam rue, and most painfully true, in the case of Thistles and Gro 
sels; “but Foxglove seeds, though minute, would hardly be carried by 
wind, an any more than those of the White Clover, which comes up 80 à! 
dantly in drained fens. sub judice lis est. And I wish’ 
young naturalists would work ied at re solution, by experim 
which is the most sure imd to find out any 
" researches in this Poste they will find puzzles € : 
wil give them oue which I s most thankful to hea 
lead 
the young student u a aes rn nd co mplex question "How s 
these i 
ids TT E plants n ie Mer the long and wi w 
mrt of the ree evn and will agree, that the whole of these is 
ong ages under an ee: rom 
divi ack to the a hea as it me ag 
drift with fresh life and verdure 
