The outside wall of the tomato, the skin, or epidermis, varies in thickness from being very thick in paste type tomatoes to being so thin as to be translucent in pink heirlooms.
The meaty interior, or pericarp, is very thick in paste tomatoes, less so, but still predominant, in beefsteaks, and even less so, in slicers and cherries. Therefore cherry tomatoes and slicers are typically juicier.
The locules are the seed chambers. Four are shown in this diagram. Cherry tomatoes typically have only two. Paste tomatoes have 2 or 3 locules. Slicer tomatoes, also sometime called Standard or Globe tomatoes, contain 3 to 5 seed cavities. Beefsteaks contain 6 or more. The seeds are suspended in a gel called locular jelly. This gel contains the sugars, glutamates, and acids that give the tomato its distinctive flavor and aromatic compounds that provide most of its aroma.
So, the tomatoes in this category, Early Slicers, contain 3 to 5 locules. They also weigh 3 or more ounces to be large enough to make nice slices, and the plants mature ripe fruit in less than 81 days after plantings otherwise it would be senseless to call them Early. The are also the tomatoes most often grown by home gardeners, earning the title Standard, and most are round without ridges, thus the moniker Globe.
Still more nomenclature.
Most Slicers are determinant. That means the vine will grow to a certain (determined) length (typically 5 feet or less), and then stop growing and producing blossoms that can set fruit. Determinant plants usually produce a short bush that requires little or no pruning and some, but not a lot of support to keep fruit off the ground. Many determinant grow well in large pots.
indeterminant plants continue growing, and producing fruit until killed by frost. The vines can grow 6 to 15 feet long and will definitely need the support of large cages or stakes. Pruning advice is a matter of individual wants and needs. Some growers like to deal with only one main vine tied to a stake, pruning off all suckers and branches. The other end of the spectrum is just letting nature take its course with zero pruning. Of course creative trellising, caging, staking or a combination thereof must be done to keep fruit off of the ground and rotting. Most Gardners prune all of the suckers and some of the branches to produce a more manageable plant. But there is no right or wrong, and the debate is hot on what method produces the most vs best fruit.
There is a third category called semi-determinant. Tomatoes in this grouping form a bush like determinants, but continue to produce fruit until frost like indeterminants. Many of these produce even shorter (3 to 4 ft tall) and more compact bushes than most determinants. A large number make good container plants. And while caging or some form of support is recommended, I have grown varieties that have strong enough stems to stay erect without any.
You are probably asking yourself, well, self, why would you grow anything but semi-determinants? And for you, that may be exactly the smart thing to do. But farmers and home canners like plants that mature large quantities all at once, or nearly all at once. Thus the harvesting and processing gets done in shorter time. Gormands and heirloom aficionados have their own favorites which spread across all three categories. To each, his own.
And about heirlooms.
Public acceptance for the label heirloom is the cultivar can be any open-pollenated tomato so long as it has been available for over 50 years including such well known tomatoes as Rutgers, Marglobe, and Big Boy even though they were F1 hybrids when first marketed, Hybrid tomatoes can become stable open-pollinated plants by repeatedly, across multiple generations, selecting offspring most like the parent plants and cross breeding them. Once all the offspring of a generation exhibit the desired traits of the original parent hybrid, a stable open-pollinated seed source has been established.
Tomato purist insist that to be considered an heirloom no tinkering with the genetic code through hybridization or engineering by commercial developers has ever been done, regardless of how long the cultivar has been available to the public.
