usdacitranges

These pictures are reproduced from the United States Department of Agriculture Yearbooks for 1904, 1905 and 1906. They were the first pictures of the newly created citranges. These fruits are hybrids of Citrus trifoliata (formerly known as Poncirus trifoliata) and Citrus sinensis, the common sweet orange.
The Rusk developed from an orange flower fertilised with Poncirus trifoliata pollen. All the other citranges shown here (plus another called Rustic) were derived from different seeds of a single trifoliate fruit from one flower cross-pollinated by sweet orange. This hybridization is considered unusual, because Poncirus is often said not to be 'zygotic', which means it does not normally form seeds by sexual fertilisation.