Hollow

Types of cavities

David Arora and M.Ya. Zerova distinguish several types of hollow stems that are key to identification:

1. Perfectly hollow (tubular): The stem is completely empty from the very start of growth and has smooth inner walls. Example: the parasol mushroom (Macrolepiota procera). Its tall, tough stem is completely hollow inside, so people almost never collect it (it's as tough as cardboard) and eat only the cap.

2. Spongy-hollow (chambered): This is a unique feature of the chestnut bolete (Gyroporus castaneus). If you cut its stem lengthwise, you'll see that the space inside isn't one continuous void but is divided by loose partitions into chambers (like a honeycomb or the pores of a sponge).

3. Hollow with age: Many mushrooms that had solid stems when young become hollow as they age, because the flesh in the center dries out and disappears. This is typical of many brittlegills (Russula).

4. Stuffed: The stem isn't completely empty, but is filled with very loose, cottony mycelium that is easily removed, leaving a cavity. Typical of many milk caps (Lactarius).

Why it matters for identification

Checking whether the stem is hollow is a very simple and reliable test.

For example, to tell first-class porcini from some other boletes, all you have to do is cut it: the stem of a true porcini is always perfectly solid and firm in cross-section, without the slightest cavity at any age. If the stem of a bolete is hollow, you are definitely not looking at Boletus edulis.