xylem vessels

[moo]

how are xylem vessels dead? surely they were alive once? i asked my science teacher who replied "because they are" which wasn't quite a good enough explaination... how did dead cells just appear from nowhere???? confused!!

[dinsdale]

In short they are not dead to begin with but die at maturity http://en.wikipedia.org/wiki/Xylem_vessel_element

[Kingaroo]

Cambium is the layer in between xylem and phloem, and it produces new cells which become inert vessels like drinking straws called xylem. Don't be hard on your teacher, my husband is a plant scientist and this is the best answer he could come up with.