How would a waxy surface on the upper epidermis of leaves prevent water evaporation?

Question

like why does the top being darker and more waxy keep it from losing more water?

Answer 1

Wax/Oil repel water. The moisture would be trapped.

Answer 2

1) Why the top surface of a leaf is Darker ( Darker green I presume ) ?

Ans.1 ) The palisade cells near the upper epidermis are full of chloropasts with green chlorophyll and are more green  in color .

As compared to the upper epidermis the cells near the lower epidermis have less chloroplast and hence pale green color .

click on the links to see -

http://extension.oregonstate.edu/mg/bota...

http://micro.magnet.fsu.edu/cells/leafti...

The cuticle is always a transparent "see through" covering , so it can show the color of under lying tissue , which is green iin the present case .

2 )How would a waxy surface on the upper epidermis of leaves prevent water evaporation?

Ans.2 ) Waxy cuticle on the upper leaf surface is a water proof coating .

It does not allow the water to escape during transpiration.

During night time stomata are , generally, closed . Still cuticualr loss of water is possible . This is prevented by a thicker coating .

see cuticle on the link below - click on the link -

http://academic.kellogg.cc.mi.us/herbran...

http://library.thinkquest.org/22016/phot...

Answer 3

the waxy layer is waterproof, so water cannot g through it and evaporate out