Al, any chance you can chime in on what accounts for "FAT" roots in cuttings that are potted up. Soil ratio, aeration etc. Can I assume fat roots means "healthy" ? Thanks.

Noss, I was referring to newly rooted cuttings that were moved the 1st time from say spaghnum moss into plastic transparent cups. From here onwards the newly form roots exhibit nice fat root growth. I think some 3 years ago there were much discussion on "fat" roots using turface, type of medium etc. Hence I thought it would be good to learn from Al  or anyone based on scientific perspective on how to achieve fat roots consistently. Right now I had a broken limb left in a 32oz cup of water and dispite neglect it grew a fat root and many branch roots.

What a good question. Most species of nonaquatic plants are able to modify root structures to varying degrees in order that they might cope with cultural conditions. I'm pretty sure you're asking after pneumataphoric roots. These are root modifications stimulated by oxygen deficit due to soggy soils, and help the roots get the O2 needed to carry on their normal work. I'll go look for something I wrote that gives a better idea of what happens.

From something I wrote for a GW Container Gardening thread:

The roots that form on cuttings rooted under soggy conditions or in water are quite different from those produced in highly aerated media (perlite - screened Turface - the gritty mix ....). Physiologically, you will find these roots to be much more brittle than normal roots due to a much higher percentage of aerenchyma (a tissue with a greater percentage of intercellular air spaces than normal parenchyma).

Aerenchyma tissue is spongy and filled with airy compartments. The compartments form as a result of highly selective cell death and dissolution in the root cortex in response to hypoxic (airless) conditions in the rhizosphere (root zone). There are 2 types of aerenchymous tissue. One type is formed by cell differentiation and subsequent collapse, and the other type is formed by cell separation without collapse ( as in water-rooted plants). In both cases, the long continuous air spaces allow diffusion of oxygen (and probably ethylene) from shoots to roots that would normally be unavailable to plants with roots growing in hypoxic media. In the case of fresh cuttings placed in water, aerenchymous tissue forms due to the same hypoxic conditions w/o cell death & dissolution.

 
Note too, that under hypoxic (airless - low O2 levels) conditions, ethylene is necessary for aerenchyma to form. This parallels the fact that low oxygen concentrations, as found in water rooting, generally stimulate trees and other plants to produce ethylene. For a long while it was believed that high levels of ethylene stimulate adventitious root formation, but lots of recent research proves the reverse to be true. Under hypoxic conditions, like submergence in water, ethylene actually slows down adventitious root formation and elongation.

Your plants need better aeration in the root zone.

Al  

Great explanation, AL. Always enjoy reading your posts sir.

Good info. Appreciate the explanation.

no, no no don't quit. I am surprise too that this branch I left in the container has at least an 8" fat root and many feeder roots. I totally neglected it. Its a branch that had broken off from one of my trees.  Rooting is the easy part. Getting them to grow in the plastic container is the challenge. I have another pile of cuttings that I left outside in the yard since November. I could see buds forming and again sheer neglect ... bucket froze many times but I guess they are resilent. I have not check for roots yet and I have walk past them many times. Honestly the rare cuttings I want them to root & grow are the ones that gives me a tough time like LSU Everbearing, Improved Celeste, Col de Dame Noir. Murphy's law.