Potato Laterals Not Just At Surface

Just after stating that 'potato laterals are mostly at surface' of the half litre plastic cup (see 'Why Are Potato Lateral Roots Mostly At Surface?'), more have appeared further down. These new laterals also at 'crest' of 'root wave' with little in gullies either side (this photo actually shows two roots, but seems to illustrate the point). Only this time new lateral growth is mostly upward and is more extensive. It is also comprised of only the finer roots, at the moment, though these possess root hairs, so might thicken up to be like those described last week.

THESE LATERALS NOT ON ROOT AT SURFACE
Far from being just beneath the surface, this root is nearly two thirds way down the cup. And it is unlikely that this part of the cup has been watered in the same way as the surface. This might indicate:

• perhaps potato roots grow in a wave fashion wherever they are, independent of soil water levels
• perhaps laterals at crest of roots are not responding to being near soil surface

IMPLICATIONS FOR GROWERS
It seems amazing that roots actually grow so close to the soil surface. This means that any sort of mechanical weeding is certain to damage them and impair the plant's ability to take up water.

Do Dahlia Roots Come So Close?
Dahlia feeder roots also come up to the surface. I wonder if they also come so close?

NO RESPONSE TO SYRINGE WATER
Still early days, but water applied by syringe to gully of root at top of cup does not seem to have produced a response, perhaps indicating laterals are not produced in response to moisture levels. Seems unlikely.