This probly falls in one of your two groups. We played with root hair cultures in the 1980's. We could grow a lot of root hairs but where only moderty successful get tops to form. Cannabis was the target. About one in five reached transplatable size. We just thought it would be fun. Lots of jars filled with roots!

While most micropropagation text books and protocols will agree with you, I will say that the classification of "axillary" and "adventious" is rather ambiguous and confusing. In my opinion micropropagation of plants should be classified into 2 categories: non-regenerative and regenerative.

Non-regenerative includes cases when we simply grow what has already been there, i.e. axillary buds, shoot tips, root tips, etc. We do not reprogram the plant tissue to dedifferentiate to a more pluripotent state, then regenerate again to become a different type of tissue. What we do is simply allow (or induce) the already formed but dormant tissue to continue to grow.

Regenerative includes cases when the tissue is dedifferentiated, then regenerated into a different type of tissue. This can be either direct regeneration such as adventious root emerged from phloem parenchyma cells, or indirect regeneration via callus, like in most other cases.

It should be noted that in micropropagation, nearly never is the root of the starting sample retained. Therefore, whether or not the procedure employs regenerative or non-regenerative method for creating the shoots, it almost always includes a stage of regenerative culture to create the root.

In micropropagation, we could produce in vitro plants by:

(1) meristem, shoot tip or nodal culture

(2) plant organ (leaf blade, petiole, rhizome, root segment, etc.) culture

Both (1) and (2) can give us the whole plant, directly or indirectly, depending on the culture conditions (chemical or physical).

Somatic embryos can also be induced, directly or indirectly, by these culture methods .

For micropropagation we can use any part of the plant either it contain meristematic cells or not. Direct and indirect embroyogenesis can help for the propagation of explant.

what about the formation of store organs like micro-tuber or micro-corms? it seems to be involved into direct or indirect organs formation

Dear Duy, adventitious and axillary are well differenced, while axillary shoots arise from differentiated tissues/organs (e. g. buds) the adventitious came from prexisting undifferentiated meristematic cells. Thus, for massive propagations the origin of shoots has important consequences. Axillary shoot regeneration has a lower multiplication rate than the adventitious regeneration; however, the possibility to occur deviation of genetic patterns are higher for adventitious regeneration than axillary.

For highly reclacitrant species and/or genotypes, the sprouting of programmed tissues/organs, as buds, isn't so easy or evident.