A Study of Tropism of Pollen Tubes to the Pistil I. Tropism in Lilium

Abstract

In the present investigation, the tropism of pollen tubes of Lilium species was undertaken intending to see a relation, if any, between this tropism and the mechanism of penetration of pollen tubes from the stigma to the ovule in the fertilization of some higher plants. Pollen grains of Lilium longiflorum were spread around the pistil slices made from other flowers of the plant, or others, and the percentage of tropism was measured. The result of the present investigation shows that the pollen tubes are attracted to the pistils on the agar medium. Therefore it is highly probable to assume that pistils contain a factor which is responsible for the tropism of pollen tubes. This factor is contained in ovary tissues not including ovules, stigmas and styles (Table I), and diffuses into the agar medium (Table III, IV) and passes the collodion membrane (Table V). From these facts it is reasonable to assume that the factor is a chemical substance or substances of relatively small molecule, at least smaller than that of Congo Red. Since the pollen tubes do not show tropism to the pistils which have been steamed at 99°C for 10 minutes (Table II), it is concluded that the active substance is metastable to heat. Similer results were obtained in L. japonicum. Extraction of the active substance was tried but it was not able to separate with 50% ethyl alcohol or ethyl-ether.