One is a critical survey of the facts
of agricultural and horticultural breeding, as they have accumulated
since the time of Darwin. This body of evidence is to be combined with
some corresponding experiments [10] concerning the real nature of
species in the wild state. The other part rests on my own observations
and experiments, made in the botanical garden of the University of
Amsterdam.
For many years past I have tried to elucidate the hereditary conditions
of species and varieties, and the occasional occurrence of mutations,
that suddenly produce new forms.
The present discussion has a double purpose. On one side it will give
the justification of the theory of mutations, as derived from the facts
now at hand. On the other hand it will point out the deficiencies of
available evidence, and indicate the ways by which the lacunae may
gradually be filled. Experimental work on heredity does not require vast
installments or costly laboratory equipment. It demands chiefly
assiduity and exactitude. Any one who has these two qualities, and who
has a small garden at his disposal is requested to take part in this
line of investigation.
In order to observe directly the birth of new forms it is necessary, in
the first place, to be fully clear concerning the question as to what
forms are to be expected to arise from others, and before proceeding to
a demonstration of the origin of species, it is pertinent to raise the
question as to what constitutes a species.
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