What is vegetable marrow which called for in a very old cookbook?

"Vegetable marrow" in an old cookbook most likely refers to courgette (also known as zucchini).

Here's why:

* Historical usage: The term "vegetable marrow" was a common name for courgettes in Britain and other English-speaking countries during the 19th and early 20th centuries.

* Similar characteristics: Courgettes and marrows are both members of the squash family and share similar culinary uses. They can be cooked in various ways, such as roasted, stuffed, or used in soups and stews.

* Evolution of terminology: The term "vegetable marrow" has largely been replaced by "courgette" or "zucchini" in modern cookbooks, but older recipes will often still use the older term.

So, if you're looking to recreate an old recipe calling for vegetable marrow, you can confidently substitute it with courgette.

However, it's worth noting that there is another squash called "marrow" (also known as "vegetable marrow") that is a distinct species from courgettes. This marrow is larger and has a tougher skin, but can still be used in similar ways.

If you're unsure which variety is intended in your old cookbook, it might be helpful to consider other ingredients and preparation methods to get a better idea.