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7.
Nucellar Seedlings

There is a characteristic of the orange and other citrus fruits (with exception of the pummelo or shaddock, rarely grown in Tropical America) which is of great horticultural importance. This is the production of what are technically known as nucellar seedlings. It is due to this phenomenon that seedling orange trees may be so much alike, not only in growth and productivity, but also in fruit characters. Oranges harvested from a hundred - or a thousand - trees in any particular region will be just about as uniform in character as those from an equal number of grafted Valencias.

Nucellar embryos arise in the following manner: after the flower has been pollinated and the ovule has been fertilized, buds develop in the tissues surrounding the embryo - the nucellus. Since these are not the result of fertilization of the ovule, but are in reality parts of the mother plant, they reproduce the characteristics of the latter just as is the case when buds or scions are used in grafting. Several of these nucellar buds may develop in a single seed. They commonly crowd out the embryo which has resulted from the fertilized ovule - the embryo which would develop into a tree not exactly like its parent. This variation is familiar to those who have planted avocado seeds - or seeds of many other fruits which have been improved by man through selection or mutation.

Of course an occasional fertilized ovule does develop into a tree, and of course trees from nucellar seedlings may give rise to new horticultural varieties through mutation. In modern times grafting has superseded the use of seedling trees in those regions where there is extensive commercial cultivation on an orchard basis. Though seedlings ultimately attain a larger size than grafted trees, the advantages of grafting are several: production at an early age,