ON LEAVES. ‘ 91 
melancholy associations which the yes have depicted in so many 
well-known stanzas. 
Nevertheless, leaves when separated from the vegetable which 
has given birth to and matured them, are not lost to the earth 
which receives them. Everything in nature has its use, and leaves 
have their uses also in the continuous circle of vegetable reproduc- 
tion. The leaves which strewed the ground at the foot of the 
trees, or which have been disseminated by the autumn winds over 
the naked country, perish slowly upon the soil, where they are 
transformed. into the /umus, or vegetable mould, indispensable to 
the life of plants. Thus the dédris of vegetables prepares for the 
coming and formation of a new vegetation. Death prepares for 
new life; the first and the last give their hands, so to speak, in 
_ vegetable nature, and form the mysterious circle of organic life 
which has neither beginning nor end. 
But let us return to the general study of leaves. We have still 
to note a last and most important phenomena in the variety of 
their functions. We speak of the spontaneous movements executed. 
by leaves under many circumstances. 
Leaves almost always assume the horizontal position. They 
have an upper surface turned towards the heavens, and a lower 
surface looking on the earth. -This position is so natural, and 
hence so necessary, that leaves take it of themselves during. day 
and night when from any accidental cause that position has been 
lost. If we place a plant in an apartment lighted by a single 
window, it is soon observed that all the leaves direct their upper 
surface towards the light. This is an experiment which our 
readers can readily repeat for themselves. But leaves perform 
other movements, equally remarkable, on which we must pause an 
instant. The study of these movements has been, as we shall see, 
the subject of some curious and interesting experiments. 
Dutrochet, having placed a young pea in a chamber lighted on 
one side only, soon observed that the leaf inclined itself towards 
_ the light, and directed its petiole towards the heavens, or rather 
inclined it towards the dark part of the chamber. The tendril was 
now nearly straight, now curved and arched, presenting very 
irregular motions. Dutrochet placed certain fixed indicators both 
over the tendril and over the petiole, and at the insertion of the __ 
