PREFERTILIZATION EVENTS IN OVULES OF PSEUDOTSUGA - OVULAR SECRETION AND ITS INFLUENCE ON POLLEN TUBES

A natural ovular secretion from the megagametophyte, essential to sexu al reproduction, was examined in Pseudotsuga. This secretion began soo n after egg formation or about 1 week before fertilization. Secreted f luid filled the micropylar canal. Morphological study showed that the fluid affected (i) dissolution of intine materials; (ii) pollen distor tion that may relate to prezygotic selection; and, (iii) induction of pollen tubes. The origin of the secreted fluid is interpreted from an experiment using homogenates. Elongated pollen supplied with a homogen ate of the megagametophyte shows immediate movement of starch grains a nd body cell. Some pollen formed pollen tubes. Homogenates of the nuce llus or the integument elicited little or no response. If ovules are d issected before the natural secretion and kept in high relative humidi ty, the micropylar canal becomes filled with fluid. This fluid is an a rtifact resulting from dissection, but is also capable of inducing pol len tubes.