[split] BAV Pal. lat. 291. De rerum naturis. 1425

[Koen G]

If we take the image literally, it is most like the Balneis buildings rather than the alcove, since the scalloped edge points down instead of up. But I'm not sure if it matters much, it is clear that architecture is placed at or over the source.

The VM examples go strongly with the "roof" part, it's even got a finial. But then this is placed on top of those scales. 
The "scales" most often stand for another type of roof or mountainous terrain.
So we can interpret the VM "pinecones" as either two roofs combined, or a roof on a mountain.

Note how the flow that comes from the VM "mountain" is different than that in the BAV MS. In the VM, many tiny "rivers" come together to form the big one. With this in mind, it seems reasonable to take the scales as mountains rather than a roof.

   

Of course, mountains don't have a roof (at least not a literal one). But what if the VM artist was used to the convention where a roofed building was drawn over a source? Imagine a text like "The x mountains are source of river y". You draw a mountain with converging little streams coming from it (as is often the case in reality), and since the mountain is a source, you slap a roof on it, finial and all.