W. H.  Lang, ?On the prothalli of Ophioglossum pendulum and Helminthostachys zeylanica?, Ann. Bot., vol. 16, pp. 23 - 56, 1902.

W. H.  Lang, ?The prothallus of Lycopodium clavatum L.?, Ann. Bot., vol. 13, pp. 279 - 317, 1899.

W. H.  Lang, ?On a prothallus provisionally referred to Psilotum?, Ann. Bot., vol. 18, pp. 571 - 577, 1904.