Le Nord : revue internationale des Pays de Nord - 01.06.1939, Page 326
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chromosomes as in the vegetative cells. After fertilization, in-
volving the union of two sex cells, the chromosome number typical
of the body is again restored. The chromosome number is not only
constant in a certain individual but is generally typical of all
members of a certain species. Comparing the chromosome numbers
of different species within a genus it is often found that these
numbers form a multiple series. The wheat genus, for instance,
is composed of a large number of varieties and forms, but these
forms fall into three distinct groups, characterized by the chro-
mosome numbers 14, 28 and 42 (i. e. 2 X 7, 4 X 7 and 6 X 7)*
This phenomenon (polyploidy) seems to be particularly frequent
in cultivated plants. In addition to wheat multiple series are
found, for example, in oats ,potato, several forage grasses, cotton,
sugar cane, banana, fruits and berries. On the other hand, some
other cultivated plant species, such as rye, barley and sugar beet,
are not polyploid but have low chromosome numbers.
It has now been found that in genera comprising cultivated
species with different chromosome numbers, those with the higher
numbers are almost always more valuable than types with low
numbers. Thus, within certain limits, there is a correlation be-
tween high chromosome number and economic importance. Under
such circumstances it is evident that an experimental increase of
the chromosome number might lead to new products of great
practical value.
Particularly during the last ten years methods have been
evolved which make it possible to induce profound changes of
this type in the hereditary constitution. Such investigations have
been going on at the Svalöf plant breeding institute since 1931-
In that year, thanks to a donation from the Knut and Alice Wal-
lenberg Foundation, a special department for cytological research
in connection with plant breeding started its activities. At present
four main methods are used in this department to produce new
types of cultivated plants with an increased number of chromo-
somes in the cells. These are the following:
1) Crosses between different species or genera and selection
of plants with deviating chromosome numbers in the progenies of
the first generation hybrids.
2) Induction of chromosome doubling by heat treatment.
3) Induction of chromosome doubling by chemical treatment.
4) Selection of plants with a changed chromosome number
among twin seedlings of different species.