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CULT: vernalization


>Bill Shear wrote:
>
>--snip  --
>
>> missing the 'vernalization'
>> needed to bloom and grow properly.
>
>Hi Bill,
>
>Could you amplify what is meant by vernalization please.

Vernalization refers to a phenomenon first noted by Gassner, a German plant
physiologist, in 1915.  He found that a period of cold temperatures was
required for the flowering of certain plants.  In his experiments, he
observed that winter rye planted in the fall flowered the following summer,
about 7 weeks after growth began in spring.  However, the same plant sown
in the spring would remain vegetative all summer and the next winter, and
would then flower on the same schedule the following year.  But by keeping
the seeds at about 35 degrees F while they were germinating in the spring,
the rye will flower the same season it is planted.

The observations have since been extended to other plants and generalized
to show that many plants must have a period of cold lasting a certain time
in order to initiate flowering when the photoperiod is appropriate.  This
is related to the need for cold to break dormancy in such plants as apples
and lilacs, but in this case it effects flowering.

In the particular application to I. versicolor, it may be (repeat, may be)
that there is such a requirement.  Thus plants of versicolor or any other
iris kept growing and warm all winter would not flower the following
spring, having missed their chilling period.

This is an adaptation that is needed because there are two appropriate
photoperiods each year which could initiate flowering in a plant.  However,
a plant that flowers normally in the spring would probably not be able to
mature its seeds if it flowered at the equivalent photoperiod in late fall.
By having a chilling requirement preceding the appropriate flowering
photoperiod, such mistakes are avoided.

You may have had the experience of buying chyrsanthemum plants in the
spring and having them flower almost immediately.  I'm not sure I remember
the correct explanation for this, but it seems to be related to
vernalization.  Can anyone help on the chrysanthemum question?

Bill Shear
Department of Biology
Hampden-Sydney College
Hampden-Sydney VA 23943
(804)223-6172
FAX (804)223-6374
email<bills@tiger.hsc.edu>






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