I first came across Marlow Moss in a paper on Mondrian by Robert Welsh here.

Moss had some correspondence with (and seemingly some influence over) Mondrian on the subject of the use of double lines in compositions. See here for more details.

The paper makes it clear that Moss is female, "Her illustrated reply ..." but I'm not so sure from the picture. [later] Definitely female, but often mistaken for male by the children where she lived the later part of her life in Cornwall.

There is what looks to be a fascinating book on Ms Moss by Florette Djikstra, reconstructing her works. It is on sale at Amazon (link) and I have a copy on order.

While waiting for that to arrive, I have found a catalogue from a 1962 exhibition at the Stedelijk Museum, Amsterdam, written by A. H. Nijhoff, from which the photograph is taken (thanks Frans Melk). The catalogue is almost entirely in Dutch, and so I am not much the wiser on her background or her gender, but it does include a number of illustrations and a brief history.

Marlow Moss

These are some of the illustrations from the catalogue      

I think the catalogue tries to list every known piece by Moss (46 paintings and 13 constructions). They are not all pictured therein.

Thanks to Mr Nijhoff. More details when available.

(Dec 2002) I notice that Mondrian scholar, Prof. Yve-Alain Bois is dismissive of MM's influence on PM,

There is a myth, circulated in part by Vantongerloo's correspondence with Gorin, to the effect that Mondrian borrowed the double line from a young English painter, Marlow Moss, who saw herself as a neo-plasticist. A few months before Mondrian adopted this new element in his art, she did in fact paint (an may have exhibited) double-line pictures; but one need only glance at Moss' earlier "double-line" pictures to  realize that she makes  very different use of this element: her couples lines are so unequal in thickness that they can be read neither as forming a single linear entity, nor as belonging to the same plane. See, for example, the two "double-line" compositions by Moss, dated 1931, and reproduced in the first issue of Abstraction-Création, dated 1932 (p. 26). It is only in the second issue of this journal (dated 1933) that one can see a "double-line" by Moss that has something in common  with those of Mondrian (p. 29); the same issue carries a reproduction of Mondrian's first "double-line" canvas (p. 31). In other words, Mondrian does not first criticize, then adopt, Moss' invention, as Vantongerloo suggests: he is at first a skeptic, then understands his lack of interest in Moss' version, then demonstrates how, and for what destructive end, he double line could be used in neo-plastic art.
Yve-Alain Bois in note 156 to an essay, The Iconoclast, in Piet Mondrian 1872-1944, Bullfinch Press, p. 371

Ms Moss should not feel too hurt or isolated by this treatment, Prof. Bois is dismissive of numerous people and publications in this essay. Nevertheless, I am still looking forward to getting a copy of his Painting as Model for Christmas.

from October 2002