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. Ver}’ 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 possilile 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 
