These are from 3 different web sites:
Apple seeds, cherry pits, peach pits, pear pips, plums pits, and apricot pits contain cyanide, which is poisonous. While a few apple seeds may not cause a problem, the effects can accumulate over time if they are given to dogs regularly. Dogs should not be allowed to chew on a peach pit, cherry pit, apricot pit, or plum pit. Chewing can allow ingestion of cyanide. Chewing could also result in the pit being swallowed, causing continuous exposure to cyanide, or could cause the dog to choke.
A dog that weighs between 40 and 50 pounds could probably eat up to 100 fruit pits without any kind of reaction, veterinarians said, but the pit could be deadly if combined with a chemical or something from another plant or medicine.
CHERRY PITS - causes a variety of effects on your dog including respiratory distress like difficulty in breathing, coughing, and sneezing