Tugudal made an observation in the Fan Grimoire thread that I wanted to explore without derailling that thread:
Can you ReHe Mushrooms to appear from (for example) dead wood, similar to the published ReAn Bees from a Lion carcass, or the fan-favourite ReAn eels from mud?
I lean towards yes, but would put on the restriction that the mushrooms created would be natural for `that peice of dead wood in those surroundings', and as such would be a random collection of mushroom types including deadly ones, so that it is not an auto success for food finding.
If this were possible I am not sure what the appropriate base would be, and if further magnitudes for selecting specific mushoom types would even be possible.
But the quality/type of mushrooms could require a further role: maybe area lore or nature/forest lore. You will not get truffles growing on a piece of pine.
Sounds reasonable if the mushrooms are appropriate just like the worms must be appropriate. I would probably work off the spells for worms to figure out a reasonable base.
I think there is little doubt that the rules allow using ReAn for "spontaneous" generation of eels from mud.
In my opinion it is a silly thing to do, and one that some people are far too eager to abuse and overdo.
According to pg. 116 of Mythic Locations, truffles are known propagate through a supernatural mechanism. The listed method of propagating them requires a Truffle of Virtue to be eaten by a creature with Magic Might 5+ and the resulting feces be used to fertilize a tree, though other sources might exist. So even if this is possible with other types of mushrooms, it might still be impossible to create truffles through Rego Herbam magic.
If you can use Rego to create mushrooms from wood, or eels from mud, couldn't Rego also make any animal pregnant? (I nearly said "woman", but humans have souls, making for a harder scenario.) My feeling is that there should be a Creo requisite for these things.
"...although Rego can make a tree bear fruit out of season, that fruit would not contain seeds, as the seeds are separate substances (potential trees) and thus creating them would require Creo." (p78). The implication is that if you want permanent seeds/mushrooms/eels, you need a Creo Ritual spell.
I'm not claiming great expertise here, I may well have missed something.
Medieval belief (in at least some circles) was that some of the more primitive creatures just spontaneously generated from the appropriate environement. Eels and frogs from mud, flies from rotting meat, mice from damp earth, spiders from air, and so on.
So since them being created from the environment was a natural process, it can be emulated by Rego magic.
For larger animals (and humans) however, they knew quite well that pregnancy involved a male and a female having intercourse. A cow doesn't just spontaneously get pregnant without any bull involved.
So no, Rego cannot make an animal pregnant by itself.
For an animal provided it was going through the normal natural process I could see rean (or ReCo for humans) making the attempt at pregnancy automatically successful.
As for mushrooms from dead wood I would say yes, but with a finesse roll to get the kind of mushrooms you want.
I am not a mycologist. I know about truffles, but I cannot tell you what specific soil/tree the next most delicious mushrooms grow in: death's trumpets or morels (I checked wikipedia on the latter, a large variety of both coniferous and also deciduous trees might do the trick).
I had the same idea initially: finesse for the type of mushroom. But finesse is more in my mind about the aesthetics or structure. It would be a rare use for a mage's area lore (or of forest/nature which would be a virtue investment).
I think finesse could choose from the types of mushrooms that grow from that particular source (not all mushrooms grow from wood), but you would probably need a lore role to know what the options are.
Ancient Magic pg. 55 establishes that a flaw in Hermetic Magic prevents it from distinguishing mother and embryo in the first trimester in most circumstances. A&A pg. 36 establishes that attempts at producing life in the laboratory have been unsuccessful. Basically, it's just a weakness of Hermetic Magic.
But even without those issues, I think the main flaw with your idea is that animals which sexually reproduce don't contain both male and female sperma. At best you could do magically assisted artificial insemination.
I agree (though I'm not sure your view of animal reproduction matches the medieval one). I'm actually arguing against the idea that ReHe lets you create mushrooms out of a piece of wood. The rules explicitly say you need Creo to create a new tree from an old one, and "there used to not be mushrooms, now there are", seems a similar case to that. I don't agree with Tugdual: I think the mushroom is analogous to the tree here.
this is my issue; they knew that trees need seeds, but mushrooms just "appear", in the same way that bees just "appear" from a lion carcass. So no creo requiste is needed. I am trying to figure out what the appropriate base is.
Well, I wanted to say "no mushrooms to mushrooms means Creo", but "leaves appear on a tree where there were no leaves before" is explicitly a thing you can do with Rego, so I take your point.
I'm still not sure I'd want it in a game I was running, but that's either a rule interpretation or a house rule.
Rego is also the Art for "[natural] process happens at an accelerated pace." It's the reason why craft magic and instantaneous transport fall under Rego. So, if people believe that bees will spontaneously appear out of cow's corpses, that's a job for Rego. Even today people probably believe that mold & fungi just spontaneously appear under certain conditions -- not realizing the ubiquity of various spores -- so it certainly seems reasonable that Rego could make that happen instantaneously, too.
There comes a point, though, where this sort of thing is stealing from other Arts too much. If you're spontaneously Rego'ing fungi from wood, you're also rotting the wood, which is bits from both Creo and Perdo. Evaporation of water happens naturally over time, so can Rego-evaporate large quantities of water? (or sublime ice?) Heck, aging is a natural process that normally falls under Perdo; can you Rego-accelerate that? It's a problem that creeps in when you start classifying spells by how they function rather than by their intent.