Comparatively few seeds germinate inside their own fruits without special, often unnatural, circumstances. For most of them that would be a bad place to germinate, although there certainly are exceptions to that rule. Tomatoes and their claose relatives are no such exception; in nature they rely on their seeds being spread by birds, or occasionally by fruit bats or other mammals (an inferior option from the point of vieiw of the plants because mammals tend to chew the seeds.)
Accordingly, many seeds have an after-ripening period during which they refuse to germinate. There are several ways in which this happens. Certain chemicals inside the seed may inhibit the cellular activity necessary for germination. Not until such chemicals have broken down can the seed germinate. This usually is months or years later, when changes in temperature, irrigation, or light trigger germination at the right season or under the right conditions.
Another variation is for the juice of the fruit to contain chemicals that inhibit germination. If such a fruit drops uneaten, it commonly will rot, seeds and all, or take years to germinate. But birds digesting the pulp effectively clean the seed before vomiting it up or passing it out in manure, ready for germination.
Tomatoes and many of their relatives are typical examples of plants adapted to such means of spreading their seeds.
