This list of "vegetarian" cookbooks was printed in the May 1910 issue of The American literary magazine The Bookman:
Vegetables and Vegetable Cooking, Mrs. E. P. Ewing, 1884. [not veg]
American Salad Book, M. DeLoup, 1901. [not veg]
Fifty Salads, Thomas J. Murrey, 1885. [not veg]
Fruits: How to Use Them, H. M. Poole, 1890.[gelatin]
Vegetarian Savouries, Mary Pope, 1904. [no preview]
Novel Dishes for Vegetarian Households, Mary Pope, 1904. [no preview]
Vegetarian Cookery, F. A. George, ??. [1908, gelatin]
The Corn Cook-Book, E. O. Hiller, 1907. [revised 1918. lard/bacon drippings/some meat]
How to Cook Apples in One Hundred Different Ways, Georgiana Hill, ?? .
How to Cook Potatoes in One Hundred Different Ways, Georgiana Hill, ?? [not veg].
Salads: How to Dress Them One Hundred Different Ways, Georgiana Hill, ??. [no preview]
Salad and Salad Making, Mrs. Emma P. Ewing, 1888. [NOT VEGETARIAN]
Fruit Recipes, R. M. Fletcher-Berry, 1907. [gelatin]
Edible and Poisonous Mushrooms, M. C. Cooke, 1894. [no preview]
The compiler of this list paid scant attention to whether the books listed were actually vegetarian cookbooks. Of the 14 listed 6 have meat dishes while another 3 use gelatin. I was unable to view any text from books noted with 'no preview'.