This may be confirmed when the seeds are
collected and sown separately in cultures that can be carefully guarded.
[99] In order to get a closer insight into the causes of this confused
condition of ordinary races, Rimpau made some observations on Rivett's
wheat. He found that it suffers from frost during winter more than the
local German varieties, and that from various causes, alien seeds may
accidentally, and not rarely, become mixed with it. The
threshing-machines are not always as clean as they should be and may be
the cause of an accidental mixture. The manure comes from stables, where
straw and the dust from many varieties are thrown together, and
consequently living kernels may become mixed with the dung. Such stray
grains will easily germinate in the fields, where they find more
congenial conditions than does the improved variety. If winter arrives
and kills quantities of this latter, the accidental local races will
find ample space to develop. Once started, they will be able to multiply
so rapidly, that in one or two following generations they will
constitute a very considerable portion of the whole harvest. In this way
the awnless German wheat often prevails over the introduced English
variety, if the latter is not kept pure by continuous selection.
The Swiss wheat-breeder Risler made an experiment which goes to prove
the certainty of the explanation given by Rimpau.
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