6 
THE AMERICAN BOTANIST. 
Few people ever imagine leaves as moving by their own 
volition. As a matter of fact, however, a vast number 
do daily move more or less in response to light or shade. 
Particularly is this true of compound leaves so called, where 
several or many leaflets are attached to a common stalk. 
Instances of such leaves are those of the rose, 
of clover, locust and horse-chestnut. Leaves of one blade 
are called simple. 
In the Pulse Family, Legiuninosac, where the phe- 
nomenon is widely prevalent, there are some leaves whose 
pinnae in closing, point forward and overlap each other; 
some where they are directed backward; some where they 
are erect and others that are pendulous. The special 
method is constant, as a rule, to the genus. It will be 
observed that in all these cases the closed condition reduces 
the leaf to the very lowest degree of expansion. This, at 
once suggests the probable cause of the phenomenon, name- 
ly to, as far as possible, lessen the degree of radiation — or 
as we loosely say, to keep the leaves warm. 
Linnaeus ever full of fancy, called the phenomenon 
"the sleep of plants", and some of the relaxed positions 
certainly suggest slumber. It may be even, that such re- 
pose is recuperative to the plant. We do not know this, nor 
can we explain or even guess at such remarkable movements 
as those of the East Indian Desmodium gyrans. This 
plant, closely related to our oAvn tick-trefoils whose jointed, 
hook-covered pods break up into lozenge-shaped parts and 
line one's clothes in autumn, as one penetrates a wild 
copse, appears to have a purposeless movement. But where 
we do not know, it is well to suspend judgment. 
This plant has a pinnately tri-foliate leaf, in which 
the middle or terminal leaflet is much the largest. This 
itself evinces some movement, but the small lateral ones are 
extremely active, keeping up an oscillating movement — and 
