Cee Evolution and Adaptation 
appear at once, and their results last only as long as the 
influences themselves last, and are then lost, leaving nothing 
permanent behind. This is true even when the external 
influences have lasted for a long time, — since the glacial 
epoch, for instance. We find, he claims, nothing that sup- 
ports the view that such influences are inherited. 
If we next examine the question of changes from zudernal 
causes, Nageli claims that here also observation and research 
fail to show the origin of a new species, or even of a new 
variety from external causes. In the organic world little 
change has taken place, he believes, since the glacial epoch. 
Many varieties have even remained the same throughout the 
whole intervening time; and while it cannot be doubted that 
new varieties have also been formed, yet the cause of their 
origin cannot be empirically demonstrated. The permanent, 
hereditary characters, of whose origin we know something 
from experience, belong to the individual changes which 
have appeared under cultivation in the formation of domestic 
races. These are for the most part the result of crossing. 
So far as we have any definite information as to the origin of 
the changes, they are the result of inner, and never of exter- 
nal, causes. We recognize that this must be the case, since 
under the same external conditions individuals behave differ- 
ently — in the same flower-bud some seeds give rise to plants 
- like the parent, others to altered ones. The strawberry with a 
single leaflet, instead of three, arose in the last century in a 
single individual amongst many other ordinary plants. From 
the ten seeds of a pear Van Mons obtained as many different 
kinds of pears. The most conclusive proof of the action 
of inner causes is most clearly seen when the branches of 
the same plant differ. In Geneva a horse-chestnut bore 
a branch with “filled” flowers, and from this branch, by 
means of cuttings, this variation has been carried over all 
Europe. In the Botanic Garden at Munich there is a beech 
with small divided leaves; but one of its branches produces 
