If happiness is a gosling recognising you and running up to say hi, then...

*best as in best for work not best for plant survival

I mean, boring first answer but corn is a classic. field corn comes in the shapes of ‘flats’ and ‘rounds’, self explanatory, where the flats are nice and flat and the rounds have more of a jagged tooth look to them, but even the rounds aren’t too bad to convince to sit still under a microscope.

Unfortunately in my job I’m not dissecting a whole lot of corn. but in terms of the stuff I DO work with, peppers and tomatoes (or anything in the solanaceae) sit pretty nice and flat regardless of size, as do pumpkins and cucumbers (cucurbitaceae), and anything from the carrot family (apiaceae), like lettuce, carrots wild and domestic, various ornamental flowers, parsnips… a carrot family seed is pretty much guaranteed to at least have one flat face to lay them down on while you work.

a lot of my job is dissecting seeds for a test called a tetrazolium test, or a TZ test. you can run a TZ test on damn near anything as long as you can expose the embryo to the chemicals in a way that lets them evenly stain. Your best case scenario, as a guy running this test, is a small amount of big, flat seeds you don’t need a microscope to see the inner flesh of, so pumpkins and stuff— but most of the stuff I’m dissecting is best done under a microscope. So, in that case, what’s easiest is anything well-gripped by forceps or with a flat face that isn’t too difficult to cut with a razor blade. Carrots have at least one flat face AND neat lines along the back that show you where you should cut, which unintentional on the plant’s part, but nice.

Grasses tend to be a little rounded on the back, and the structures to aim to cut through are on the front flat face, so they can be a little tricky but ultimately aren’t too bad, although they need more attention and time the smaller the species is. Asters are pretty round but tend to be conical with some kind of point, so they’re not rolling everywhere, those also aren’t too bad.

Getting to the weirder stuff, though. Wildflowers vary incredibly based on the family, shape, and size, oh my god. Asters (the sunflower family, asteraceae) tend to have big structures on either end that keep them in place, but listen: THEY ALSO CAN BE EMPTY. When I’m actively counting plant embryos and putting them in chemicals, a seed that’s supposed to have an embryo and doesn’t is something that counts against the sample, as in, for the purposes of the test I have to mark it down as a dead seed that didn’t even have the chance to prove itself by changing colors in a chemical soup. Depending on how domesticated they are, this can end up being a significant chunk of the sample.

Brassicas, that is, mustard seeds and the wider brassicaceae family of kale, Brussel sprouts, that sort of thing…. These are ROUND. they DO roll everywhere. Often they’re big enough to be able to handle with forceps comfortably enough, especially once they’ve soaked up some water in the preconditioning stage of the test, but they ARE breaking free of my grip and attempting to escape. The smaller the very-round seed, the more crazy it can get with it.

The smaller the seed in general, the harder it is to cut. Catnip is hard because it’s both very small and has a hard, kind of brittle seed coat to it; BUT it also has a flat-ish face and two characteristic ‘eyes’ on one end, which make it easy to tell which side to cut. Also one that tries to disperse itself while cutting, because the hard seed coat makes it flick away into the aether that much easier. Basil is annoying because it has the same oblong ‘little black seed’ kind of thing going on, BUT it has no markings to guide a cut with a razor blade, AND, as some basil enjoyers may know, it makes a gelatinous goo when exposed to water. Cutting basil seeds with a razor blade for this test means notching the middle while simultaneously cutting through the layer of mucus, which makes the seed stick to the forceps and whatever surface you’re using to cut them on under the scope. they are not getting away, but they aren’t enjoying it, either.

along those lines, the smallest seeds we do. At a certain point the industry guidance does away with trying to cut them with razor blades and instead advises poking through the seed coat with a sewing needle attached to a metal handle. Poppy seeds— oh my god, you can only imagine. Little tiny herbs like feverfew are kind of crazy, stuff like seedbox (winter primrose family), too.

About once every other week, my coworkers and I get a weird little plant or flower I’ve never heard of in my life, from a plant family I’ve never read about, and we’ll be at the TZ handbook planning an Apollo 13 mission on something named like… yknow how Victorian British guys named flowers, ‘winter’s last blushing kindness’ or something that says distressingly little about the creature itself. I’m not complaining by the way it’s just baffling every time. you CAN run a tetrazolium viability test on damn near anything— I once put larkspur seeds with mites on them into TZ solution, and the mites’ bodies had stained red when I pulled them out. that was crazy.

(I should have explained this earlier. the point of the test is that the cells that are still breathing inhale the solution and undergo a reaction that stains them red, so you can see which tissues are alive. In the case of seeds, we compare the staining pattern to a handbook that says what is and isn’t acceptable as a living seed. an embryo that stains red in a certain way can be called dormant instead of dead, even if it didn’t germinate in the germination test. we want things to turn red! red means a higher score!)

I’ve also done TZ tests on sheep’s sorrel, a seed from polygonaceae with three flat faces, which was difficult not because it couldn’t sit flat, but because the cuts the book prescribed were kind of odd and complex for the shape of the seed, and the three flat faces were hard to grip with forceps. all sorts of stuff can get TZed and be hard for interesting and unforeseen reasons.

I think the hardest thing to cut for this test is German chamomile, actually. It has layers. Not only is it incredibly small to the point the sewing needle risks doing significant damage to it if you pierce it wrong, the embryo itself is in a sac that shifts around a little within the seed once it’s hydrated, so actually piercing both the seed coat and the anatomy holding the embryo is pretty challenging, especially when not pushing hard enough just causes the seed to roll to one side of the head of the needle (and yknow, the size means it sticks to it a little with the surface tension of moisture being what it is… it’s a whole thing.)

the smallest seed I’ve ever seen TZed was at my last workplace, by my old boss. she had to check to see if the orobanche seeds she recovered from a sample were still alive; orobanche is a parasitic, extremely invasive plant with a ‘dust-like’ (literal technical term) seed, and checking samples of crop seeds for it means literally washing them and passing the water through a series of sieves, then putting the resulting leftover residue of dirt and chaff to dry on filter paper, and checking for them manually under a microscope. My old boss had found some in a sample (incredibly rare, only time I’ve ever seen an orobanche test come back positive), and if they were proven to still be alive, it would have repercussions on where and how the company could legally sell that seed lot in the US. She did a TZ test on them— I really doubt she cut them, actually, the seeds are way smaller than the tip of a sewing needle, I’d assume she put them in the solution whole and sieved them back onto filter paper— and the seeds were, in fact, still alive and staining red. Saw it with my own two eyes. It was crazy.