Thanks Walt.
The term "smokey bubbles" is just a convenient adjective that I coined to describe their milky appearance - it's not scientifically significant.
Sometimes these bubbles are present and sometimes not and to be honest I don't know for sure what the bubbles are or indeed how persistent they are. Initially I thought they might be filled with spores waiting distribution by rain splash or similar. However another possibility is that they are guttation drops.
See here:
http://en.wikipedia.org/wiki/Guttation
As to why...
well I'm not at all certain about this but I believe that guttation (in certain fungi) serves to reduce the amount of water in the cells to prevent the cell wall rupturing during freezing weather.
...but the bottom line Walt, is that I don't really know

!
Bruce
