FRITZ MULLER, in a letter from St. Catharina, Brazil, dated January 9, has given me some remarkable facts about the movements of plants. He has observed striking instances of allied plants, which place their leaves vertically at night, by widely different movements; and this is of interest as supporting the conclusion at which my son Francis and I arrived, namely, that leaves go to sleep in order to escape the full effect of radiation. In the great family of the Gramineae the species in one genus alone, namely Strephium, are known to sleep, and this they do by the leaves moving vertically upwards; but Fritz Muller finds in a species of Olyra, a genus which in Enlicher's “Genera Plantarum” immediately precedes Strephium, that the leaves bend vertically down at night.