A section in Pleistocene gravels at Barnwell, Cambridge, was described by Prof. Marr & Miss E. W. Gardner in 1916. They drew attention to the occurrence there of peat-seams yielding definite plant-remains, which were submitted to the late Clement Reid for identification. His preliminary report, showing the Arctic nature of the flora, was incorporated by Prof. Marr in a paper read before the Geological Society; but, unfortunately, death prevented Mr. Reid from undertaking the full examination of the beds which he had, no doubt, intended to make. I lately had the opportunity of investigating the Barnwell pit, and the examination of fresh material revealed the existence of a far larger fossil flora than was suspected originally. The records of such Arctic floras in low latitudes are few, and in the present instance a number of plants identified had not been recognized previously in the fossil state. It was thought desirable, therefore, that the results of this fuller study should be placed on record, in order that they might be available to other workers in the same field. Owing to the great kindness of Mrs. E. M. Reid, I was able to use the unique collection of recent seeds made by Mr. Reid in his lifetime, and that collection (referred to as the Reid Collection throughout this paper) was the standard for all my systematic work. As the stratigraphical details were dealt with in 1916, no full account of the beds is given here, but the accompanying section, drawn to scale,