3 
A 
‘ 
7 
4 
4 
ON LEAVES. ~ 97 
the night was observable in a considerable number of vegetables, 
and that in the absence of light, plants quite changed their 
physiognomy, so that it became very difficult to recognise them 
from their bearing. He further states that it was the absence of 
light:and not the nocturnal cold which was the principal cause of 
the phenomena, for plants in hot-houses closed themselves during 
the night just like those which were exposed in the open air. 
He recognised also that this difference is much less apparent in 
young plants than in more matured ones. 
The illustrious Swedish botanist made many observations on the 
diversity of position that leaves affect during the night, and he 
has even attempted a classification of these differences. The most 
general idea which he sought to establish, was, that the positions 
differed according as the leaves were simple or compound. Linnzus 
thought that the object in these circumstances was to place 
the young shoots under shelter from nocturnal cold and from 
the effects of the air. It is among the composite leaves, in short, 
that the difference between the waking and sleeping is most clearly 
indicated. 
The folioles of the Trefoil stand erect, curving in a longitudinal 
direction in such a manner as to form a sort of cavity or cradle. 
The folioles of the Melilotus are half erect, but divergent at their 
summits. In the Oxalis, Fig. 124, the folioles usually rest upon 
a common petiole, in such a manner as to turn their lower surfaces 
inwards, and show only their upper surfaces. In the Bladder 
Senna (Colutea arborescens) the folioles rise vertically in such a 
manner as to rest perpendicularly upon the common petiole, the 
upper surfaces turned towards each other. The Cassias have, on 
the contrary, the folioles depressed and folding back on the lower 
surfaces. The folioles of the Mimosa rest the,length of their 
petioles in the direction of their summits in such a manner that the 
two extreme folioles are directed forward, folding back upon their 
upper surfaces, and the others falling upon the back of the folioles 
which range near the summit. 
The leaves of the Orach root (Atriplex hortensis) fall back upon 
the young shoots and enclose them, as if to protect them from the 
effects of the atmosphere. The Chickweed closes its leaves during 
the night, and _ opens them in the morning. The Evening 
H 
