5o6 



THE POPULAR SCIENCE MONTHLY. 



bend up so much tliat they press against the stem ; and, on looking 

 down on one of these young plants from vertically above, the lower 

 surfaces of the leaflets are visible : and thus their upper surfaces, in 

 accordance with the general rule, are best protected from radiation. 

 While the leaves on this young plant were thus behaving, those on an 

 old bush in full flower did not sleep at night." 



Again, "the species of Melilotus sleep in a remarkable manner. 

 The three leaflets of each leaf twist through an angle of 90, so that 

 their blades stand vertically at night, with one lateral edge presented 

 to the zenith " (Fig. 8). We have no room for the description of the 



c. 



Fig. 8. Melilotus officinalis: A, leaf dHrin? the daytime; B, another leaf asleep ; C,a leaf 

 asleep as viewed from vertically above, but in this case the terminal leaflet did not happen to 

 be in such close contact with the lateral one as is usual. 



complicated movements performed by these plants. Their petioles and 

 sub-petioles are continually circumnutating during the whole twenty- 

 four hours. Their cotyledons do not sleep. 



The nyctitropic movements of eleven species of Trifolium were 

 observed and were found to be closely similar. If we select a leaf of 

 Trifolium repens having an upright petiole and with the three leaflets 

 expanded horizontally, the two lateral leaflets will be seen in the even- 

 ing to twist and approach each other until their upper surfaces come 

 into contact. At the same time they bend downward in a plane at 

 right angles to their former position, until their midribs form an angle 

 of about 45 with the upper part of the petiole. The terminal leaflet 

 merely rises up without any twisting, and bends over until it rests on 

 and forms a roof over the edsjes of the now vertical and united lateral 



