Inferiority is Complex

Some botanical terms ring of judgment. One example is the pairing of superior and inferior, basically indicating “above” versus “below.”

Images of flax flower (on left – a superior ovary) and cranberry (on right – an inferior ovary) from Gray’s School and Field Book of Botany, 1887, captured from BHL

Those words can be heavily loaded in literature and street language, associated with evaluation and assessment. Analyzing Goldsmith (in comparison to Johnson), Isaac D’Isreali concludes: “He might have thought, that with inferior literature he displayed superior genius, and with less profundity more gaiety.” (Miscellanies…, New York, 1841, Rare Books 124749)

Relative position permeates fiction, as with Pip’s observations in Great Expectations: “At the time when I stood in the churchyard, reading the family tombstones, I had just enough learning to be able to spell them out. My construction even of their simple meaning was not very correct, for I read ‘wife of the Above’ as a complimentary reference to my father’s exaltation to a better world; and if any one of my deceased relations had been referred to as ‘Below,’ I have no doubt I should have formed the worst opinions of that member of the family.” (Rare books, first edition, 3 volumes, 122367)

In the more objective world of plant biology, the terms superior and inferior are purely positional, absent emotion. Description is matter-of-fact, avoiding the truth that location is not the simple development you might imagine from descriptions of a flower’s ovary; if the ovary is inside the flower, atop the sepals, petals, and stamens, it’s simply superior.

Botanists present the superior ovary as the normal condition, to some extent because it’s what we see in the earliest flowering plants, but also because plants with superior ovaries, such as tulips, oranges, and tomatoes are straightforward and easy to explain. The floral stem (the receptacle) produces whatever parts it will, and then retires to a nice life, enlarging as needed to support any maturing fruit.

When petals and anthers are shed from a developing Orange flower, you readily see the pistil (with its globose, green ovary) developing inside the flower, at the very tip of the receptacle (the stem that produced and holds the flower parts)
A Tomato flower, part of which was sliced away in order to show the entire pistil (ovary, style, and stigma), with the green, globose ovary developing at the tip of the floral stem – superior to the point at which sepals, petals, and stamens are attached.

If, however, the sepals, petals and stamens are on top of the ovary, if the ovary appears beneath remaining flower parts, then it is inferior. Search the web and you’ll find many simple illustrations of inferior ovaries that attempt to explain development. But the situation is more complex when you cut into flowers, searching to understand structure and sequence in development. Most critically, regardless as to whether the ovary is deemed superior or inferior, anatomists tell us the flower generated its pistil (including the seed-bearing ovary) at the tip of the receptacle, which means any sepals and petals were formed (botanists say “laid down”) before-hand.

It’s a morphologist’s challenge to determine how an ovary, which necessarily forms at the flower tip, appears below the stamens, petals and sepals that were produced earlier. For some of the simplest examples, we look to the Cucurbits (Cucurbitaceae, the melon family, including squashes, pumpkins, cucumbers, gourds, etc.)

A squash flower, with its inferior ovary that promises to mature as a yellow crook-neck.

Even though a Cucurbit flower apparently tops its ovary, we know for certain something happened to reverse positions. We see this in many groups of flowering plants, but the method varies, and that has been an issue for botanists: “The problem of interpretation of the inferior ovary has been one of the most controversial and long-debated topics of plant morphology.” (Kaplan, 1967)*

In the case of melons and squashes, the answer may lie in its the receptacle (the floral stem), which doesn’t behave like the stem in orange and tomato flowers; it holds unwavering devotion to an inferior habit. At least, we learn from Judson’s 1929 study of cucumber** that he believes early in bud development, receptacular tissue mounds around and tops the ovary.

Imagine a developing flower in which the receptacle doesn’t go into semi-retirement once it has initiated a pistil. Rather, while on some hormonal trip, the stem is directed to completely wrap around and above the ovary, carrying other flower parts with it, up-ending the apparent order in the process. Sepals and petals, which most textbook floral diagrams show below the terminating ovary, are now above. According to Judson, this is how you have melons, cucumbers, pumpkins, and other kinds of squash.

An illustration from Judson’s 1929 anatomical and morphological study of Cucumber flowers, in which he demonstrates the tissue surrounding the ovary is part of the stem.
Judson’s diagram, showing that the veins that are part of the sepals and petals peel off above the ovary, at the tip of the receptacle: (SPB) secondary petal bundle, (MSB) main sepal bundle, (MP petal bundle, (CP) bundle extending into the receptacular tissue surrounding (NVS) the nectary vascular system, (SC) stylar canal, (PBB) bundle extending f placental bundle to the placenta, (PB) a placental bundle, (CCB) bundle of the s cylinder within the back of a carpel, (0) bundle extending to an ovule, (VP) the vascular plate.

Other researchers would support the idea that pepos (Cucurbit fruit) are formed by floral tissue (sepals, petals, and stamens) growing together around the ovary. That idea and Judson’s are summarized as an “appendicular theory” supporting floral segment origin and the “receptacular theory” insisting on Judson’s stem origin. It isn’t simple, and remains something of a mystery.

Beyond inferiority, melons and squashes harbor other secrets. Practically all are vining, and are generally “monoecious” – which means the vine produces two kinds of flowers, pollen-bearing (male) and pistil-packing (female.) Gardeners know this, they’ll tell you that only flower buds showing an ovary underneath will yield fruit. Check out the cucumber below – there she blows, or grows.

Newly opened female flower of an ‘Edmonson’ cucumber. In the photo below, you’ll see a male flower.
Newly opened male flower of the ‘Edmonson’ cucumber, easily identified by its lack of an ovary. Flowers develop and open sequentially in each cluster, with male flowers developing first. This is the reason the first flowers on almost any Cucurbit are thought of as “sterile” – they develop anthers with pollen, but no ovaries that will become fruit.

Cucurbit fruit have their own terminology; they’re called pepos. In cross-section, you’ll note seed develop in fertile zones (typically three) along the thick inner fruit wall, rather than from a central axis. This becomes especially obvious in pumpkins and gourds that turn hollow at maturity.

Cross-section of a Kiwano Horned Melon, showing seed emerging from fertile strips (placentae) to fill the fruit. This character (termed parietal placentation) is part of what it means to be a pepo.

Culinarily, melons are known for their refreshing taste; almost every ancient culture cultivated one or more kinds.

A silly watermelon carving on a cruise ship buffet
A $100 gift Cantaloupe for sale in Japan

We readily think of cantaloupe and watermelons, perhaps because of their size and color. But the most appreciated of the family might be cucumbers, which have been cultivated and loved for millennia.

Cucumber ‘Suyo’ in The Huntington’s Brody Potager

Though common, there’s something eccentric about cukes. I learned, unexpectedly, that some artists have featured cucumbers in decorative motifs, particularly Carlo Crivelli (c. 1430-1495), who seemed to hang a cucumber in almost every sacred image he created. Perhaps the fact that the Italian word for cucumber, cetriolo, is just a bit similar to his own name meant the cuke became Crivelli’s way of planting himself in the paintings.

Cucumber, garlanded with other fruit, in Carlo Crivelli’s 1485 painting “The Dead Christ With the Virgin, St. John and St. Mary Magdalene,” at Boston’s Museum of Fine Arts. See:
https://eclecticlight.co/2016/02/20/carlo-crivelli-and-his-cryptic-cucumbers/ and
http://albertis-window.com/2019/01/crevellis-cucumbers-and-cotan/

More horticultural, and intensely literary, I was delighted to discover William Cowper’s didactic poem “The Garden”, in his fascinating book The Task …***(Huntington Rare Books 124137). Written in response to a simple challenge, Cowper demonstrates his ability to poetize the most seemingly mundane topics. In “The Garden” he includes an extensive description of the gardener cultivating hothouse cucumber crops. Some excerpts:

Raising Cucumbers....
 To raise the prickly and green-coated gourd,
So grateful to the palate, and when rare
So coveted, else base and disesteemed—
Food for the vulgar merely—is an art
That toiling ages have but just matured,
And at this moment unessayed in song...
The seed, selected wisely, plump, and smooth, 
And glossy, he commits to pots of size 
Diminutive, well filled with well-prepared 
And fruitful soil, that has been treasured long ...
Indulged in what they wish, they soon supply 
Large foliage, overshadowing golden flowers, 
Blown on the summit of the apparent fruit. 
These have their sexes, and when summer shines 
The bee transports the fertilising meal 
From flower to flower, and even the breathing air 
Wafts the rich prize to its appointed use. 

“My words fly up, my thoughts remain below: Words without thoughts never to heaven go.” Shakespeare’s Hamlet

References:

*Donald R. Kaplan, 1967. “Floral morphology, Organogenesis, and Interpretation of the Inferior Ovary in Downingia bacigaluph.” Amer. J. Bot 54(10): 1274-1290 https://www.jstor.org/stable/2440367?seq=1#metadata_info_tab_contents

“A study of the early stages and of the vascular arrangement (cucumber) indicates that the outer tissues of the inferior ovary are of receptacular nature, and are not made up of the fused bases of sepals, petals, and stamens.”

**J. E. Judson, 1929. “The Morphology and Vascular Anatomy of the Pistillate Flower of the Cucumber” Am. J. Bot 16(2): 69-82 plus plates. https://www.jstor.org/stable/2435882?seq=1#metadata_info_tab_contents

***The Task and other poems, William Cowper. free Project Gutenberg ebook, 1899 edition: https://www.gutenberg.org/files/3698/3698-h/3698-h.htm

See Also: Awkward Botany, Citizen Botany for the Phytocurious – “Hand Pollinating Cucurbits”. https://awkwardbotany.com/tag/cucurbitaceae/

Halloween pumpkin carving has gone in different directions over the past few years

Leave a comment

Leave a Reply

%d bloggers like this: