Fig. 4. Representative photomicrographs of Gregg 65 cotton pollen incubated at 28°C for 180 min on the pollen germination medium with surrounding relative humidity (RH) levels of 35%, 50 to 80%, and 100%. Pollen tube elongation was reduced at 35%, and pollen tubes ruptured in a 100% RH. Maximum pollen tube elongation occurred between 50 and 80% RH.