Here's a paragraph from an article about that tree.
Facing the inevitable loss of the parent navel orange tree in its dedicated park, a decision was made by the University of California scientists to try to save this tree by inarching. The tree had been girdled by gummosis and was rapidly deteriorating. The inarching was done by Dr. H. J. Webber, H. W. Mertz and Glenn Blackman. They inarched with seedlings of sweet orange, rough lemon and sour orange. The gummosis lesions can be seen in the lower trunk just above the top of the protective cylinder. Dr. Klotz again photographed the inarches on July 17, 1944, twenty six years after the initial inarching was done in 1918 and the inarches are shown on the right in Fig. 4. In 1951, it was noted that some of the original inarches showed lesions of Phytophthora. Therefore, in that same year, a second inarching was done using three seedlings of Troyer citrange and one of trifoliate orange. The grafting was done by Denard C. Wylie, Senior Superintendent of Cultivations at the Citrus Experiment Station.
The survival and preservation of the parent ‘Washington’ navel orange tree was dependant on the successful inarches made in 1918 and repeated again in 1951. This same fungus killed its sister tree at the Riverside Mission Inn in 1922. However, the timely inarches saved this historic tree. The tree was in good health and bearing a good crop of fruit.