Date: Tue, 2 Jun 1998 21:25:12 +0100 From: "S.Gordon" <na05@rapid.co.uk> To: cp@opus.hpl.hp.com Message-Id: <aabcdefg1886$foo@default> Subject: Re: Stratification
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>Hi all , Sorry , but i have to defend my last posting as i speak from
>experience
>
>Tim posted:-
>
>>Some additional points to clarify my original posting on
>>stratification:
>>
>>1. Seeds must be stratified moist. Dry stratification is not effective.<
>
> Quite right ,they need water, oxygen and chilling.
>
>
>>2. The change in the seed is chemical in nature. It is NOT the
>> imbibing of water and oxygen. Water and oxygen reach their max
>> levels in the seed during the first few days.<
>
>
> You miss the point ,you do not get the chemical reaction without the
>intake of water and oxygen. The imbibition of water initiates the enzymatic
>processes that results in the breackdown of stored compounds for their
>mobilization to various sites within the seed. This chemical reaction takes
>more then a few days.
>
>
>>3. Stratification is only effective between 32 and about 50 F.
>> Temperatures below freezing cause the chemical reaction to
>stop.
>
>
>I think thats what i said , although your upper limit can enhance dormancy
>in some seeds.
>
>
>
>>4. The time required for complete release from dormancy is independent
>> of temperature or species. It requires between 2 and 3 months.
>
>Try telling that to species with epicotyl dormancy.
>
>
>>5. If freezing improves germination times, it is because freezing
>> causes micro-cracks in the seed coat which improves the rate
>> of water uptake. 2 minutes in water at 140 F is optimal for inducing
>> micro-cracks. See Deno's book for the exact procedure.
>
>Water uptake i thought you said it is a chemical reaction!
>These appear to be pre-stratification treatments and would be ok for seeds
>you would normaly scarifiy but would be useless for seeds with embryo
>dormancy
>
>best wishes
>
>steve , liverpool, uk.
>
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