Why's palm stems equally thick all the way?

[Bastula]

I've been wondering, why is palm stems equally think all the way from bottom to top when other regular trees are thicker at the base and become smaller further up towards the top? Also, why doesn't palms have tree rings?

Regards,
Blastula

[JackBean]

I'd say because they are monocots, so they should not secondary grow, similarly like grass.

[JackBean]

basically as I said
http://en.wikipedia.org/wiki/Palm_%28pl ... Morphology