How do flowers transform into fruits in fruit bearing plants like tomato etc. while this is not the case in other flowering plants like Jasmine etc.?

In general, flowers transform into fruits in a process called, ‘fertilization’. Although the fertilization process is mostly similar in all the plants, the presence of reproductive organs in flowers and the pollination process may greatly vary among the plant species.

For example, the male and female reproductive organs are present in the same flower of a tomato plant; whereas separate male and female flowers are present in the same pumpkin plant. But, the palmyrah has separate male and female trees. Hence, for a simple understanding, let us consider tomato plant as an example in this answer.

The female reproductive organ has an ovary. The ovary contains ovules (egg), which develop into seeds upon fertilization. On top of the ovary is a long tube, called style. The tip of the style is called stigma, which is usually sticky or hairy in nature.

The male part of the flower also has a long filament on which the anther is present. The anther produces the yellow, dust-like pollen grains that contain the sperm cell. During the process of fertilization, the pollen grain first lands on the receptive hairy or sticky stigma.

The pollen grain then germinates and grows a pollen tube. The growing pollen tube reaches the ovary through the style tube, and penetrates the ovule through a tiny pore. After fertilization, the ovary will develop into a fruit and the ovules will develop into the seeds.

Sometimes, a barrier called ‘self-incompatibility’ interrupts the normal fertilization process. The pollen germination, pollen tube growth or ovule penetration is halted at one of its stages in plants having self-incompatibility.

Most of the jasmine species has strong self-incompatibility as well as cross-incompatibility. Hence, the chances of natural fertilization and fruit formation are very less in jasmines. However, fertilization and fruit formation successfully take place in jasmine hybridization programmes. Usually, jasmine fruits contain only one seed.