Boll
/bəʊl/
Definition 1 of 2
Pro Tip 1/3Plant Case
Boll refers to the protective spherical case around seeds of certain plants. 
Look at how the bolls protect the seeds inside.
Pro Tip 2/3Agricultural Term
Most commonly used in agriculture; especially when discussing cotton or flax. 
During harvest, farmers check if the bolls have opened.
Pro Tip 3/3Mature Boll
A 'mature boll' indicates that the fruit case has ripened and seeds are ready. 
The field is full of mature cotton bolls.