I looked at over a thousand pictures of Gladiolus without finding a match soI wrote to Tony Avent to ask what this is and he said he thought it was Gladiolus byzantinus but was forwarding my e-mail to Scott Ogden for confirmation. Here's the e-mail I just got from him:
Margaret:
Attached is the confirmation on the glad id from Scott Ogden.

>Tony-
> >Bingo. It's definitely the common old form of Gladiolus
byzantinus, the
>desirable heirloom cultivar, 'Cruentus', not to be confused
with the
>inferior pinkish forms now commonly schlepped around in the
Dutch trade.
> These usually bloom with
bearded irises
>here in mid-April & thrive on heavy soil.

>-Scott

Tony Avent

Thank you all so much for the responses, it was a hard one to find!

Nigella, aren't you lucky! That is a gorgeous plant! I was just reading an article in the latest issue of Garden Ideas & Outdoor Living (one of those Better Home & Gardens specialty mags) where they have an article on pg 48 on antique bulbs, titled "Yesterday's Bulbs for Today's Gardens".

There's a short paragraph on the history of glads, as well as hyacinths, tulips, dahlias (didn't know that of the 10,000 varieties enjoyed by the Victorians, only 3 still exist!), lilies, daffodils and cannas.

Not a long article, but enjoyable and a lot of nice pictures. I'm inspired to find the little dwarf canna 'Atom', which looks gorgeous! It's always nice to try to keep these older plants around.