456 LOTSY, EVOLUTIE-FACTOREN. 
Het trof mij aangenaam te ervaren, dat Dr. BRIERLY eene Over- 
eenkomstige meening huldigt, betreffende de verondersteld erfelijke 
veranderingen, zoo vaak van lagere organismen en fungi, door 
wijzigingen in de cultuurmedia, vermeld. 
If, zegt Dr. BRIERLY 1), the change be in the physiological con- 
stitution of the organism, it is a fact of incalculable import, for it 
would mean that the physiological constitution of an organism 
could be altered at will, the facility and scope of change increa- 
sing with fuller knowledge and finer technique so that theoreti- 
cally there is no limit to its operation. But the only foundation 
which we can find for any systematic categorisation of living orga- 
nisms is the absolute constancy of their physiological constitution, 
this being the ultimate specific criterion. If therefore one may at 
will transmute one physiological constitution into another, it follows 
that one can change one species into another species, and this 
with great rapidity, merely by the simplest adjustment of the most 
common environmental factors. But it is perhaps not sufficiently 
realised that our culture media, our testtubes and flasks are but 
microcosms, and that the little experiments divised in laboratories 
have been carried out on an infinite scale by Nature for aeons 
of centuries. That whereas in laboratories we merely change a 
medium from saccharose to dulcite and back again, or raise the 
temperature by ten degrees or perform some other equally trivial 
operation, Nature offers to microorganisms infinite permutations 
and combinations of all the physico-chemical factors operative on 
this earth. If therefore the little endeavours of human investiga- 
tors may so easily change one species into another species, Nature 
must surely be doing this on an infinite scale! But to admit that 
species in Nature are unstable and labile, one instant moving in 
this direction, the next instant moving in that, as the world adjusts 
itself, is surely a reductio ad absurdum. Were it true a science of 
biology would be a Utopian dream; more we should not exist for 
evolution had been imposible.” 
Het komt mij voor, dat BRIERLY gelijk heeft: evolutie vereischt 
een stabiliseerend, zoowel als een verandering veroorzakend, element. 
Mij schijnt het, dat het element, dat gedurende lange perioden 

1) Transactions British Mycological Society. Vol. VI. p. 
