In olive-culture grafting is universal. When the sapling is about seven years old it is cut down to the stem, and a shoot from a good tree is grafted upon it. Three years later it begins to bear fruit, its produce gradually increasing until about the fourteenth year. No tree under cultivation is allowed to grow ungrafted; the fruit in such case being inferior. Grafting is alluded to only once in Scripture (Ro 11:17 etc.). St. Paul compares the coming in of the Gentiles to the grafting of a wild olive branch upon a good olive tree: a process 'contrary to nature.' Nowack (Heb. Arch. i. 238) says that Columelia's statement that olive trees are rejuvenated and strengthened in this way (see Comm. on Romans, by Principal Brown and Godet, ad loc.), is not confirmed. Sanday-Headlam say (CC International Critical Commentary on 'Romans,' p. 328): 'Grafts must necessarily be branches from a cultivated olive inserted into a wild stock, the reverse process being one which would be valueless, and is never performed.' 'The ungrafted tree,' they say, 'is the natural or wild olive,' following Tristram, Nat. Hist. of the Bible, 371