Comment by Jedd | Hacker News Reader

Comment by Jedd | Hacker News Reader

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> The freefall of grapefruit from 10 m does not damage the pulp[1] because pomelo peel consists of vascular bundles and an open-pored cellular structure with the struts made of parenchymatic cells.

I have a Marsh grapefruit tree, fruiting now (southern hemisphere) as it happens, and I note that it produces particularly pithy progeny. (Ignoring for the moment that Pomelo is one of the parents of the modern grapefruit.)

I don't have a convenient 10 metre drop to test this, and while I have no reason to doubt the veracity of this citation, I'm now consumed with curiosity why this plant has evolved to have this feature.

I expect it's quite an expensive adaptation, and given that modern specimens are the result of a lot of cross-breeding over the years to have juicier pulp and a lower ratio of skin/pith to pulp (ie. reduced resistance to damage) it presumably was even more expensive in ancestor plants.

Standard fruit purpose is to have animals unwittingly propagate the plant -- entice something to eat the fruit, and some time / distance later, deposit the seeds in a fertiliser ball. How does protecting the pulp from these kind of damage assist with that -- unless ancestor trees were spectacularly tall, and ancestor consumers fantastically fastidious on fruit quality.

[1] https://doi.org/10.1088%2F1748-3190%2F11%2F4%2F045002

While researching a reply, I uncovered USDA Technical Bulletin No. 1413: "Thermal Properties and Heat Transfer Characteristics of Marsh Grapefruit". Please enjoy:

https://hortscans.ces.ncsu.edu/uploads/t/h/thermal__51bf44b0...

Goodness, that is interesting.

It's not clear why this matters from the paper, in that it sounds like (but not spelled out) that they are perhaps trying to refrigerate fruit for transport, where the transport itself is not actively refrigerated, merely insulated, so the reduction to target temperature has to occur before shipping. However this was published in 1970, and I'd assume in that part of the world refrigerated shipping and (large) storage was not uncommon?

Aside #1 - undamaged grapefruit will happily store at room temperature for 6 weeks or more, and be the tastier for it.

Aside #2 - received wisdom is that grapefruit, and perhaps most citrus, benefit from one or more frosts to 'sweeten up', though I have never understood the mechanisms for this claim, or how high-water fruit does not burst its vesicles and then deteriorate rapidly.

TFA and this paper you cited may speak to the latter (the fruit content does not freeze overnight as the thermal inertia is so high), and might partially debunk the former.

(absorbed by osmosis during my time at Zest, a JIT produce handling company)

Harvest time is extremely hectic. There's a very small window to get months worth of produce picked, sorted, cooled, packed and shipped. Cooling is a major bottleneck, because capital for refrigeration is not unlimited. Likewise any delay can be a major issue- if a truck is slow to load, how do you know whether or not you need to re-cool your produce first?

It's well known what temperatures produce does well at (can't be too hot or too cold without MAJORLY affecting end margins) because it's easy to test by setting a fridge to a given temperature. It's much harder to know, for a given type of produce, how fast it will cool or heat, and how long you need to spend doing that. It's not as simple as sticking a thermometer in it, which will create paths for heat to move into and out of the produce. Even then you still don't know what the heat distribution inside the produce is so you can optimize the temperature over as much of the plant as possible.

It's really quite tricky and stuff like this helps farmers a lot. IMO farmers do more actual number math more than almost any other occupation (ex: [1]). Much of it is rules of thumb and guesstimation, but they still are constantly balancing dozens of figures to make choices every day. They're always doing mental calculations in economics, biology and physics. Even if the job wasn't so physically and technically taxing, I would respect the hell out of them just because of the mental workload.

[1] https://youtu.be/ywBV6M7VOFU?t=630

And here am I the doofus who works in Accounting Software often saying "I should have done something with fruit" when my work involves too much math for my liking.

I'll try to stop using that from now on, thanks!

I heard (no refernece, sorry) that oranges do from green to orange when the temperature drops. Apparently colour change does not affect taste, nor necessarily indicate ripeness. Would anyone knowledgeable please chip in and correct or elaborate on this please.

> produces particularly pithy progeny

> fantastically fastidious on fruit quality

Great alliterations. Great writing all around. This just made my night.

I'm always amazed by the Anglo-Saxon attraction for alliterations :-)

Amazing alliterations always achieve admiration.

Asonance also allows adulation.

Wow didn't realize it till you pointed out. It's like I just had a Princess Caroline moment watching Bojack Horseman

Don't miss proPagate the plant!

Seconded. This could have been written by Churchill.

Actual Churchill quote would be "My dear you are inedibly bitter, but tomorrow I shall be sober and you will still be inedibly bitter."

Not Churchill, alas. https://quoteinvestigator.com/2020/06/28/drunk/

Maybe a damaged fruit would rot before the animals got to it, becoming offputting?

I have a 5-6m high grapefruit tree, and they... do not survive the fall. This material sounds cool but I hope it's better than my grapefruit.

Pomelo has a bit of a different ratio of rind to fruit than most grapefruit.

https://en.wikipedia.org/wiki/Pomelo#/media/File:Citrus_gran...

> This material sounds cool but I hope it's better than my grapefruit.

Flavor-wise it undoubtedly is.

"I'm now consumed with curiosity why this plant has evolved to have this feature."

Grapefruit didn't evolve naturally. In fact, it's only a couple of hundred years old. It's the way it is because of human intervention.

Absolutely. I also have a pomelo tree, though it's still in a pot in the shadehouse, and produces a single (enormous) fruit each year.

Grapefruit are a cross, probably, of pomelo and a sweet orange - as you say, not all that long ago. While some grapefruit varieties are quite pithy, pomelos (that I've seen) are very pithy - hence the 'this can only have been even more expensive a protective layer in earlier versions of this plant'.

The question still stands - why is this adaptation useful, given it's probably expensive. (That assumption of mine may be entirely wrong.)

Early species would have been shorter, and all species in the history of this would have fruited long before the individual trees reached 10 metres (I'm guessing even in ideal conditions that implies 10+ years growth). Most would-be consumers of the fruit would be able to reach fruit within the first metre or so (if unable to climb or fly) and anywhere in the tree otherwise.

Interesting. There are other fruit & seeds out there that develop strong exocarp or mesocarp (think coconut) and I believe it has to do with wanting the fruit to travel longer distances to encourage geographic spread. The plant probably "prefers" that the seedlings take hold some distance from the parent, so wants the seed preserved longer and taken away by certain kinds of animals (hairless apes!)

What kind of animals live, or lived, in wild citrus' native range? Now I'm curious. [EDIT: Himalayan foothills... Macaques? Elephants?]

Or it's selected for particular animals as spreaders? In wild grapes, for example, most are adapted for bird spread (small dark acidic berry, high up in a tree on dangling shoots) but there are a handful of species (vitis labrusca "fox grape" for example, and vitis rotundifolia aka muscadines) that have adapted for mammals and they are quite different: larger berry, lighter colours, strong smell (think Concord), lower acids, slip skin, and a tendency to "shell" (fall off the vine when ripe). They also tend to grow wild in shadier moister areas, e.g. the underbrush where foxes and skunks and racoons etc. will grab them, not birds.

All I'm finding is 'south east Asia' as origin -- which is an enormous range of fauna.

I understand the 'travel far and wide', though of course evolution's not directed, and is there significant difference in fitness & success over the long term for a variation that allows a plant to produce offspring 1km away in one generation (say 5y), rather than taking 2 generations?

(And, of course, it's worse than that. The 10m drop potential isn't realised until the plant is probably 15 years old or more -- at which point the distance / propagation calculation is almost irrelevant, as that specimen would have produced fruit for at least 5 years whose seeds would have travelled the same distances, regardless of this (future) robustness capability.)

Sadly, though, I suspect plant archaeologists have more pressing concerns than this question.

Gotta love HN; I click comments and am met with screenfulls about grapefruit.

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I’d say throw it up to the appropriate height. You don’t need exactly 10m and it’ll replicate the drop event perfectly.

Note to grapefruit tossers: Please practice safe science. If you're going to throw an object 10 meters straight up in the air and see how it impacts the ground, you need to not be the ground it impacts, or at the very least your science will be ruined, if not your day as well.

If we learned anything from Lawn Darts, it was this.

Maybe.

Those who survived lawn darts learned nothing.

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