This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
For a fruit juice to make a good jelly by boiling with the addition of sugar only, the juice must contain a sufficient amount of a substance called pectin and also sufficient acid. Some fruit juices will not make acceptable jelly by this method because they are deficient in pectin, whereas others do not contain enough acid. In the middle states west of the Mississippi River the fruits most commonly used to make jelly without addition of pectin are apples, crab-apples, blackberries, sour plums, grapes, currants, and gooseberries. During the winter months cranberries are used extensively.
Cruess and McNair have reported that the following fruit juices contain sufficient acid and pectin to produce good jelly: blackberries, loganberries, Isabella grapes, Tokay grapes, cranberries, currants, whole lemons, and pomelos. They state that oranges have enough pectin but not always enough acid. Apricots and cherries sometimes make jelly but are usually deficient in pectin. Pomegranates and strawberries have enough acid but lack pectin, and pears, peaches, and huckleberries lack both pectin and acid. Citron melons and mission figs have enough pectin but lack acid. They state that lemon is too high in acid to produce a good jelly, but that two whole oranges and one whole lemon make a good combination, the acidity of the lemon allowing for the deficiency in the orange.
By the addition of pectin and sugar, all fruit juices, so far as the author knows, can be used for jelly.