here. My major influence in horticulture, my maternal Grandfather, had a few grafted plants in his garden, including a three variety Pear tree. This sort of grating can enable a small garden to provide a larger range of varieties in smaller amounts than from three individual trees.
The scion is normally the same size or slightly thicker than the rootstock, particularly if the rootstock is used to inhibit the growth of the scion variety, as the picture shows. A quick pause here to elaborate on that last sentence. We have all either tried or been tempted to try growing a fruit tree from a seed we've found in fruit we've been eating. If you have ever been successful, one thing that would be immediately noticeable would be the size and vigour of the tree. In their natural state, most if not all our popular fruit crops can rapidly reach staggering sized plants. The problem with this is that you need a very large area to grow just one tree and you need a very long ladder to reach the fruit!Secondly, Apples for example do not come true from see. This means the pips produced from one fruit will not grow to produce the same fruit as the parent from which that original pip came. It is the same as human genetics. A child from any parents will never be an exact clone of either parent. As such, all Apple stock has to be increased by vegetative propagation. By taking cuttings, grafting or division. Every specimen of Granny Smith or Bramley is in fact a slice from the original seedling. Only one of each variety has been grown from a seed. That is the plant that first produced the apple which some gardener thought was good enough to share and reproduce.
Some species are grafted to produce taller trees for ease of cultivation as the species in nature may grow as a low spreading bush making harvest and disease control a problem.
Roses tend to be grown on rootstock because it allows a faster production of commercial varieties and also allows for less hardy varieties to flourish in colder areas. In many instances, climbing or rambling roses for example, the natural growth on their own roots is far too aggressive for garden use.
I just know I can look forward to many years of fresh juicy Pears in the future!