Outside in the yard poking around the plants for photo ops yesterday, we stumbled upon early indications of a burgeoning bumper crop of what cooks call vegetables but botanists call true berries, garden variety tomatoes (Solanum lycopersicum*), AKA love apples. We'd picked up a couple of impressively large, robust-looking plants from Hannaford's in York Corner over Mem Day weekend, and Tuck had transplanted them into large terra cotta pots set out on the sunny eastern terrace, topdressing 'em with our homegrown compost mixture, Chelsea Gold. According to the ID tag, our tomatoes can be expected to grow to 3.5" across. The newborn above (x 4), still wet behind the ears, clings to the spent floral parts of its parents, sheltered by the pubescent sepals that once enclosed the perfect flower — male and female parts in the same blossom — from whose loins it sprung.
According to the National Gardening Association, shaking the tomato plant increases fruit production by more evenly distributing pollen.
The rationale behind shaking their booties to increase production has to do with anatomy. We hadn't noticed before, but the structure of the business end of a tomato flower is somewhat different from that of your typical flower, a four-part structure of whorls starting from the base and working upwards, including a calyx of sepals, a corolla of petals and then, as Wikipedia explains (click here for diagram):
Androecium (from Greek andros oikia: man's house): one or two whorls of stamens, each a filament topped by an anther where pollen is produced. Pollen contains the male gametes.
Gynoecium (from Greek gynaikos oikia: woman's house): one or more pistils.The female reproductive organ is the carpel: this contains an ovary with ovules (which contain female gametes) … The sticky tip of the pistil, the stigma, is the receptor of pollen. The supportive stalk, the style becomes the pathway for pollen tubes to grow from pollen grains adhering to the stigma, to the ovules, carrying the reproductive material.
This cross-section of a sedum from an earlier post illustrates the typical floral anatomy, with male parts whorled individually around the central female parts. Look inside a rose or a daylily blossom and you'll see a variation on the theme.
Anatomy of a tomato flower from "Insect Pollination Of Cultivated Crop Plants," self-described as "The First and Only Virtual Beekeeping Book Updated Continously." Unlike the separate stamens of the typical flower, the tomato flower's male parts are fused to form a tube embracing the female parts. "The construction of the anthers, delicately united with the filament, permits them to vibrate at the slightest touch and send a rain of pollen down the cone outlet and around the stigma."
"Various tests in greenhouses have proven that the tomato flower is not self-pollinating," according to "Insect Pollination Of Cultivated Crop Plants" and other online sources:
However, if the inflorescence is shaken, the pollen will fall from the anthers onto the stigma, and fertilization will result. One pollen grain is needed for each seed, so many grains are needed on each stigma. Incomplete pollination results in misshapen fruit. Cool or cloudy weather retards pollen shedding (Stoner 1971). Growers of tomatoes in greenhouses use various types of vibrators or other devices each few days to shake the flower clusters.
More from Wikipedia:
That tomatoes pollinate themselves poorly without outside aid is clearly shown in greenhouse situations where pollination must be aided by artificial wind, vibration of the plants (one brand of vibrator is a wand called an "electric bee" that is used manually), or more often today, by cultured bumblebees.
Potato-leaved tomato (above) is a German heirloom "of a rather primitive type as seen in the flowers," where the stigma extends beyond the anthers, writes the proprietor of the Danish blog In the toad's garden. "Mainstream tomato flowers have a shorter style [that] ends inside the anther barrel. As the pollen sheds from the anthers, it drops directly to the stigma at the end of the style, inside the barrel … Potato-leaved tomatoes with the longer style hold the stigma out of the barrel, out where pollinating insects rule, in the world of cross breeding." (In the toad's garden photo)
Checking out our own tomato flowers, pictured here with another of the babies, we noted they are of the "mainstream" type with stigma contained within the tube of fused anthers or "anther barrel," as described in the previous caption. 'Wonder whether a determined bumblebee could have its way with them anyway? "As tomatoes were moved from their native areas [in South America], their traditional pollinators (probably a species of halictid bee) did not move with them," says Wikipedia. "The trait of self-fertility (or self-pollenizing) became an advantage, and domestic ['mainstream'] cultivars of tomato have been selected to maximize this trait."
Don't want to shake your tomato plants? Let the buzz-pollinating bees do it. Pollinator.com has an x-rated description of their technique:
Did you ever watch a bumblebee work a tomato blossom? When it does, it pulls the flower down into a vertical position, puts its fat belly against the stigma, and buzzes. The pollen that is released will fall by gravity (since the flower is now tilting down) directly to the bee's fuzzy (and statically charged) belly, which is rubbing against the sticky stigma as it vibrates. Tomatoes are self-fertile, but the pollen can come from any other tomato that the bee has visited, a bane for seed growers who want to keep varieties pure, but lovely for the gardener who wants fruit.
Update: Do Maggie's cows dream of electric voluntary milking systems?
*Linnaeus was right: "The scientific name for the tomato in general use for over two hundred years was Lycopersicon esculentum. However, molecular studies in the past fifteen or so years have helped to shift the name back to the one originally assigned by Linnaeus, Solanum lycopersicon," according to the UBC Centre for Plant Research.