28 
YORKSHIKK NATFRALISTs' UNION. 
adaptable with great powers of accoimuodatioii to a variety of 
circumstances, in fact, their powers of accommodation or adapt- 
ability exceed those of all oiher plants : they are dominant over the 
world, and are present in every latitude of the globe and, moreover, 
it is the only flora that is so, so that it is only by fortuitous circum- 
stances that the weaker and more primitive vegetation of other 
regions can obtain a precarious and temporary lodgment within the 
region ; such lodgments l)eing most freciuently observed in acjuatic 
species, which, owing to the constant dredgings of our canals and 
waterways, obtain footholds in the new soil which is from time to 
time exposed. 
Although untold millions of seeds and spores of plants are annually 
produced, yet that few survive, is shewn by the relative numbers of 
the different species only slightly fluctuating from year to year, so 
that a number equivalent to practically the whole of the new genera- 
tion is regularly destroyed — and this e(iually applies to animal life — 
KiG. 10. Floristic map of Europe showing the identity in distribution of the Flowering 
Plains with that of animal life, the same region evolving the dominant or most highly advanced 
Floral lif*" and pursuing precisely the same migratory route from Europe (after Prof. Drude). 
The Rku indicates the regions occupied by the predominant or Central European group 
and shows also the practical identity of their line of advance into Asia with that of animal life. 
The Blue represents Drude's West Siberian flora, which in Central Europe is being driven into 
the mountains, and is also shown to Ije in process of being cleft into a Northern and Southern 
.u;roup by the advance eastward of the more dominant races which have succeeded them. Purplf 
denotes the flora known as Mediterranean or South European. Yellow indicates the flora of the 
steppes or of Turkestan, and Green denotes an earlier form of the Mediterranean type which 
overspreads Asia Minor, etc. 
so that the natural extension of the range of any species within its 
native region is very slow, so slow indeed that it has been computed 
by Fliche that the Beech occupies 25,000 years to spread 250 miles, 
while the Scots Pine needs 50,000 years to spread the same distance, 
the enormous length of time consumed being probably due to the very 
slight differences in dominating powei- of the competing trees, so that 
