Went to check wild plant damage from the recent freeze.   Interesting how there is worse trouble out in natural areas than “in town,” a demonstration perhaps of the “urban heat island effect”  arctic blast protection by buildings, hedges, and fences.   The shrub damage out in the boonies is dramatic.

Checking the vitals of damaged twigs, I thumbnail-scratched the thin outer bark skin off of a few expecting to find a nice living green layer as in most healthy branchlets.  But Pond Apple exposed an outer bark surprise.

Pond Apple by John Bradford

As you may know, PA is a swamp creature. Plants in floody places cope variously with  periodic or perpetual wet feet.   Big problem:  sustaining life where sogginess smothers normal life processes.   Ventilation becomes a special challenge in the wet world,    Soooo, to get to the point, scratching revealed a ventilation trait in Pond Apple new to me and kinda fascinating, at least to somebody with not much more going on. Upon scratching off  the topmost bark skin, Pond Apple reveals the pretty wavy grille you see on the left below.  The dark curvy lines are firm “wood.”   The light areas in between are soft and porous.   If you cut across the branch you find that those soft porous cups are the expanded ends of wood rays.   Wood rays are soft living veins  extending deep into the wood.    They function like my veins, helping to “circulate” water, nutrients, starch, and dissolved gases.   Hey, I like this vein analogy.   My veins meet the air in my lungs.    It looks like the Pond Apple “veins “  meet the air via those soft cup areas which  funnel air directly into the wood rays.  The outer bark seems to work as a big lung. That must helps with swamp ventilation. 

Left. The bark outer surface with skin removed. Light porous cups between wavy walls of dark wood. Right. The thin outermost skin is at the far left. The cups are seen cut across, with the red lines pointing at the outer edge of one cup. The rays connected to the cups are seen extending into the wood. The border between bark and wood is the dark curved vertical line along the center of the photo near the cup bases.

Now, a pest might say, “can’t you have air enter other trees through the bark, and wouldn’t rays have to broaden or be broken up as the branch expands?” Sure, in fact, the little corky “lenticel” spots  on branches allow gas exchange.  But it looks like swamp Pond Apple took that subtle commonplace ability and exaggerated it up into air injection turbosupercharger  for life in the wet zone.