Calder continued working at Glasgow and published several more papers on Carboniferous lycopods in 1933 to 1934.
In 1938, Calder worked on the seed plants Calymmatotheca kidstonii and Samaropsis scotica, both from the Tournaisian age (345.3 to 359.2 million years ago) of the Lower Carboniferous (Mississippian) [REF].