Function. Plants also have a pH rating. Plants whose pH matches the soil's pH can take up nutrients more efficiently than plants with a pH rating different than the soil. Pine trees and the needles that they produce prefer acidic soil.
Price of a Stamp. The current price of a first class stamp is 49 cents. A domestic first class letter (1 oz.) is 49 cents. The price of each additional ounce is 21 cents. It will cost you 34 cents to send a domestic postcard.
@anon39270, the stamps only hold the value that you originally purchased them for. i.e. The current price for a forever stamp is .44 cents (2010) so 20 years from now the value of that same stamp will still be .44 cents, even if the price for one ounce is $2 then. So, you would need five forever stamps from this year for 1 ounce in 20 years.