Re: How do plants breath?

Plants do not have lungs but passively exchange gases, mainly oxygen and carbon
dioxide, through tiny pores in their leaves and young stems termed stomata. Each
stoma consists of two guard cells. Stomata can open and close by swelling and
shrinking their guard cells, respectively. Plants need to limit gas exchange to
prevent excessive loss of water vapor via transpiration.  

Older stems having openings termed lenticels. Lenticels cannot close.

Plants usually produce more oxygen then they require, via photosynthesis.
However, all plant parts continually use oxygen for cellular respiration in
mitochondria, just as our cells do. Some plants have tissues with large
intercellular air spaces, termed aerenchyma. This allows internal movement of
oxygen from aboveground parts to underground, nonphotosynthetic parts such as
roots, rhizomes, corms, tubers and bulbs 

If you search madsci.org or google.com for the terms mentioned above, you can
find a lot more information such as photos, size and number of stomata,
aerenchyma and lenticels.