Neighbor offered me a scrounge...

[3fordasho]

Every sort of wood has them. They're just bigger and more easily visible in oak.

Ok, then easily visible medullary rays usually mean oak in my area... I've not noticed them in green or white ash, american, slippery or siberian elm, hard or soft maples, hackberry, black cherry, willow, cottonwood, black or honey locust, mulberry, or anything else I've run across, except local varieties of Oak.

 

[Jon1270]

Chainsaws leave end grain rough enough to obscure all but the hugest rays, but if you made a clean cut with a tablesaw (or a utility knife) you'd be able to see them on many of those woods without magnification. You can also see them as flecks of contrasting color on radial split surfaces -- again, they're much larger with oak, where the "flecks" are more like patches, but you can easily see them in the elm, hard maple, cherry, locust, and mulberry -- look for small lines perpendicular to the grain. They are pretty much invisible in poplar, soft maple and probably some of the others. Pockets of ray cells in oak can be inches tall and maybe close to a sixteenth thick, which is orders of magnitude larger than most other woods.