EFFECTS OF OVULAR SECRETIONS ON POLLEN IN PSEUDOTSUGA-MENZIESII (PINACEAE)

Effects of ovular secretions on pollen grains were examined in Pseudot suga menziesii. The exine is cast off in the micropylar canal. A membr anelike structure covers parts of pollen grains and appears to protect them. The outer intine consists of fibrous materials, but it also sho ws a thicker filamentous appearance in some ovules during pollen elong ation. The inner intine is electron-dense. Its fibrous nature is occas ionally visible. Dissolution of the outer intine varies in amount and manner in ovules from different trees. The plasma membrane near the po llen wall alternatively appears normal and distorted. These different morphologies of the outer intine and of the plasma membrane are consid ered to result from secretions from the ovule. The outer intine may co ntain electron-dense globules that are formed in the tube cell and tra verse the inner intine. Pollen tube formation appears to be triggered by a secretion from the ovule. Cross-pollinated grains are less distor ted compared with self-pollinated grains.