Is this a root on grafted Gymnocalycium mihanovichii?

[keithp2012]

I had a grafted Gymno fall off as the bottom species rotted. Coming out of the gymno body bottom was a long, thick, white root like growth. Was this a live root? The cactus had green on the body, if I planted the cacti right away will that "root" absorb water and grow new roots, allowing the cacti to live degrafted? Do I plant in dry or moist soil?

[esp_imaging]

Coming out of the gymno body bottom was a long, thick, white root like growth. Was this a live root?

Possibly! A photo would help here.
If its long and straight, it would just be the remaining vascular bundle from the stock still attached. The roots look like: http://davesgarden.com/guides/pf/showimage/282134/

The cactus had green on the body, if I planted the cacti right away will that "root" absorb water and grow new roots, allowing the cacti to live degrafted? Do I plant in dry or moist soil?

If it's root, it should be OK. Use dry soil, give it a week or so before watering (if it's winter where you are, maybe don't water at all until spring, unless you are keeping it somewhere warm). If not, you will have to root it as a cutting - keep it fairly dry, warm and shaded.

[keithp2012]

Coming out of the gymno body bottom was a long, thick, white root like growth. Was this a live root?

Possibly! A photo would help here.
If its long and straight, it would just be the remaining vascular bundle from the stock still attached. The roots look like: http://davesgarden.com/guides/pf/showimage/282134/

The cactus had green on the body, if I planted the cacti right away will that "root" absorb water and grow new roots, allowing the cacti to live degrafted? Do I plant in dry or moist soil?

If it's root, it should be OK. Use dry soil, give it a week or so before watering (if it's winter where you are, maybe don't water at all until spring, unless you are keeping it somewhere warm). If not, you will have to root it as a cutting - keep it fairly dry, warm and shaded.

I don't understand what a vascular bundle is? I thought it was a single root from the gymno that grew into the bottom stock fusing them together. If seperated will the vascular stock act like a root and absorb nutrients from the soil or should it be cut off and the method you mentioned after used? I don't have a photo I was referring to an old cactus I had.

[esp_imaging]

I don't understand what a vascular bundle is? I thought it was a single root from the gymno that grew into the bottom stock fusing them together.

The vascular bundle is the main collection of vessels which transport nutrients, along with tough, fibrous supporting structures. In Hylocereus (and columnar / globular cacti in general) it's the central cylindrical core of the cactus. A graft involves the vascular bundles of the stock and scion fusing, so nutrients and water can pass from the stock's roots to the scion. It doesn't involve the scion rooting into the stock (although this can happen).
In a rotting Hylcoereus, the much tougher vascular bundle is likely to be quite persistent after the soft tissie has rotted away. A cutting woudl need all the unhealthy tissue, including the vascular bundle, cutting away to root successfully.

[keithp2012]

I don't understand what a vascular bundle is? I thought it was a single root from the gymno that grew into the bottom stock fusing them together.

The vascular bundle is the main collection of vessels which transport nutrients, along with tough, fibrous supporting structures. In Hylocereus (and columnar / globular cacti in general) it's the central cylindrical core of the cactus. A graft involves the vascular bundles of the stock and scion fusing, so nutrients and water can pass from the stock's roots to the scion. It doesn't involve the scion rooting into the stock (although this can happen).
In a rotting Hylcoereus, the much tougher vascular bundle is likely to be quite persistent after the soft tissie has rotted away. A cutting woudl need all the unhealthy tissue, including the vascular bundle, cutting away to root successfully.

Got ya now, thanks for explaining!

[7george]

A photo would help us much. And if that Gymnocalycium is chlorophyll-less, no roots will save it.