The Reaction of the Stigmatic Tissue against Pollen-Tube Growth in Selfed Self-Sterile Plants

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Abstract
East and Humphrey, in studies on Nicotiana, found that the speed of growth of pollen tubes within the styles of self-sterile plants varied and that certain depressed growths of the tubes resulted in failure of fertility, while compatible matings show rather constant exhilarated growth. Fertility of incompatible matings occurs in flowers pollinated in early bud and increases during the late flowering season. Pollinations made after normal opening of the flowers and before approaching maturity commonly fail. As staining material 0.5% thionin in 20% alcohol made the ends of the pollen tubes observable under magnification of 600 diameters. The greatest depression of growth occurred in a certain stigmatic zone of interference. It is assumed that fertility in early bud occurred because of greater pollen tube growth under high nutrition. "End-season" fertility is presumed to occur because the flowers at that stage fail to produce adequate amounts of the substances causing incompatibility. The nature of these substances was not determined, but the depression of tube growth was associated with certain globules appearing within the cells of the stigmatic tissue 24 to 48 hours before the flowers were due to open. These globules stain reddish-brown with thionin. These studies corroborate previous reports given in Genetics 3, 353-366 (1918), and in Proc. Nat. Acad. Sci. 20, 225-230 (1934).

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