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Figure 1. 

Diagram of the double fertilization and fertilization recoveries. The successful fertilization by the first-emerged pollen tube results in the fusion of the persistent synergid cell with the fertilized central cell, leading to a dilution of the pollen tube attractants so that no more pollen tubes are attracted. If the double fertilization by the first-emerged pollen tube fails, however, the persistent synergid cell remains viable and continues to produce pollen tube attractants to attract a second pollen tube to salvage the fertilization, i.e., the synergid cell-mediated fertilization recovery that cause the degeneration of the persistent synergid cell. When the two pollen tubes fail to fertilize and both the synergid cells are nonfunctional, the two central cell-secreted peptide signals, SAL1 (SALVAGER1) and SAL2, are in place to draw additional pollen tubes to the ovule for fertilization, i.e., the central cell-mediated fertilization recovery.