818 THE AGE OF SOME EXISTING SPECIES OF PLANTS. 
officinalis L., Rubus fruticosus L., Cornus sanguinea L., Euphorbia 
in the J apanese Flora. Eight species, while found with the pe 
enter also into the “bee akong flora, extending to North Africa 
these are Thalictrum minus L., T. flavum L., Ranunculus re pens 
Stellaria aquatica Scop., Corylus Avellana L., Potamogeton trichoides 
Cham., Zannichellia palustris L., and Cladium Mariscus Br. ; while 
Potamogeton heterophyllus Schreb. has the same distribution, except 
that it has not been found in N. Africa. With a 8 ane distribution 
Menyanthes trifoliata Ls Stachys cileuneis = ‘Revewasks navies 
L., R. Acetosella L., Betula alba L., Scirpus pauciflorus Lightt., 
Taxus baccata L., and Isoetes lacustris ris L.) extend round the north 
Pree gee —_ while three (Lycopus europeus L., saliedad Plantago 
L., an ragmites communis Trin.), aving the same distribution in 
the 
€ various vied conditions which necessarily affected ori 
species in their diffusion over such large areas of the earth’s 
ce in the course of, say, 250,000 years, should have ted 1 to the 
production of many varieties, but the uniform te estimony of the 
remains of this considerable pre-glacial flora, as far as the materials 
ne. of @ comparison, is that no appreciable change has taken 
0 carry the history of any existing = keer of pee: 
bepond the sina deposits. ex: oft he plant remains from 
Tertiary strata have been referred ee still living one) but the 
examination of the materials, as far as they have come before me, 
convince me that this — been dies without sufficient evidence, 
ee _ conditions existing during even the colder of the 
periods i 
oe = fosn ‘oy no warmer ~varte of the earth 
ies now exist, though floras of the e 
cies ee nes taining closely ied species. The sedimentary 
beds at the base of ial Epoch ornergse a a at 
present know, the earliest remains of any e xisting species of plant. 
It is not my purpose to point out the bearing of these facts on 
_ any theoretical views entertained at the present day; I wis. 
aicaly to place them before the members of this section as data 
_ which must be — — account in constructing such theories, and 
as confirming the long-established axiom that by us, at least, as 
workers }, Species must be dealt with as fixed quan tities 
