Like you might have studied. Heated hair expands while colder air contracts. So, the sound isn't able to move as efficiently in cold air than it would in warmer air.
<em>characteristics that are always present in well-developed living organisms are
</em><u><em>1 digestion
</em></u><em><u>2 excretion
</u><u>3 growth
</u><u>4 respiration
5 reproduction
6 circulation of nutrients and food
senses are also present...
</u>
</em>
Moisture. The answer is moisture. Stratification is only possible due to the moisture being trapped with the seeds.
