554 The Ohio Naturalist. [Vol. VI, No. 8, 



A DIURNAL ROTATION IN LEAVES OF MARSILEA. 



Robert F. Griggs. 



It has long been known that the leaves of the various species 

 of Marsilea "go to sleep" at night. The change of position at 

 the beginning of night is very conspicuous and definite, resem- 

 bling that of Oxalis and the clovers. It is caused by a bending 

 of the petiolules which bend up at night so as to close the leaflets 

 together thus affording protection from exposure. The occur- 

 rence of such strikingly similar movements in these three plants 

 which have no inter-relationships nor similarities other than the 

 accidental resemblances of their leaves is a very remarkable 

 coincidence. 



So far as the writer has found this day and night motion is 

 the only one that has been reported for Marsilea. But in addi- 

 tion there are under certain conditions at least, very conspicuous 

 changes of position in response to light stimuli, which are of 

 considerable interest. 



During the summer of 1904 the writer was engaged in some 

 work for the United States Department of Agriculture which 

 took him to Victoria, Texas. While located at that place he 

 frequently had occasion to visit the government experimental 

 farm located about a mile from the town. Very often instead 

 of following the road he took a short cut across the fields. The 

 land is low, swampy at times and in places is covered with 

 Marsilea vestita. On these plants the observations recorded 

 below were made. Unfortunately other business intervened so 

 that it was not possible to make visits to the plants as frequently 

 as would have been desirable to test the universality of the 

 occurrence of the phenomena nor has it been possible since to 

 repeat them. But on account of their interest I venture to 

 publish them for what they are worth. I copy the original 

 notes, with only minor changes, from my note book as they were 

 written at the time. 



At six o'clock on the evening of July 14, as I was coming 

 across the fields from the experimental farm to Victoria I saw 

 great numbers of Marsilea vestita Hook, and Grev. The leaves 

 were still open and in every case turned to face the setting sun 

 in such a manner as to catch the rays perpendicularly. They 



