Each tomato flower has both male and female parts. Male organs called stamens are illustrated in blue. The female organ, called the pistil, consists of a style and an ovary (shown in pink).

Nearly all tomato lines, including today's modern varieties, are self-pollinating. In other words, the pollen from each flower's stamens fertilize only the ovary of the same flower.

Isolation of these male and female parental lines is not necessary. Male plants can be planted as close as 2-m from female plants. 

There are a few exceptions. Currant tomatoes (Lycopersicon pimpinellifolium) and potato-leaf types of L. esculentum generally have styles that protrude outside their blossom. These lines are more attractive to insects and thus, more likely to be cross-pollinated. Netting or caging to exclude pollinating insects is required if any of these types are used as female lines. Also, do not collect seeds of double fruits since double flowers are more prone to insect pollination.