[Plant-biology] Re: grafting plants from different families?????

[monique]

Generally, only very closely related plants can be grafted--scion and 
stock from the same species or genus.  Rarely are intergeneric grafts 
successful.  Your tomato/eucalyptus scenario is probably impossible.

I don't think your method of "grafting" will work.  A successful graft 
requires fusion of two cambium layers, not penetration of the stock by 
scion roots.

A good book on horticultural techniques--plant propagation--will 
probably answer your questions.

M. Reed